Threading reference
Tap Drill Size Chart
Find chart-based pilot drill diameters for common metric, UNC, and UNF threads using cutting taps. Each value shows its source and 75% theoretical full-thread reference basis.
Find a verified chart row
Tap Drill Quick Lookup
Enter a supported metric, UNC, or UNF thread designation. Results use the same records as the charts below.
Examples: M6 · M8x1.25 · 1/4-20 · 1/4-28
Enter a thread size to see its chart reference.
Reference tables
Tap Drill Size Charts
All listed drill diameters are chart references for the stated theoretical thread percentage. Use the individual source context and tap-maker guidance for the job.
Showing 60 of 60 listed specifications
Metric Tap Drill Chart
Metric coarse and selected fine pitches, M2–M20.
| Thread size | Pitch / TPI | Tap drill | Approx. converted | Applicability | Verification | Source |
|---|---|---|---|---|---|---|
| M2 × 0.40 | 0.40 mm | 1.60 mm | 0.0630 in | Cutting-tap reference · 75% theoretical full thread | Cross-checked, consistent | Haas 2024Guhring |
| M2.2 × 0.45 | 0.45 mm | 1.75 mm | 0.0689 in | Cutting-tap reference · 75% theoretical full thread | Cross-checked, consistent | Haas 2024Guhring |
| M2.5 × 0.45 | 0.45 mm | 2.05 mm Manufacturer reference difference: Haas 2024 lists 2.05 mm (approximately 0.0807 in); Guhring lists #46 for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 0.0807 in | Cutting-tap reference · 75% theoretical full thread | Difference disclosed | Haas 2024Guhring |
| M3 × 0.50 | 0.50 mm | 2.50 mm | 0.0984 in | Cutting-tap reference · 75% theoretical full thread | Cross-checked, consistent | Haas 2024Guhring |
| M3.5 × 0.60 | 0.60 mm | 2.90 mm | 0.1142 in | Cutting-tap reference · 75% theoretical full thread | Cross-checked, consistent | Haas 2024Guhring |
| M4 × 0.70 | 0.70 mm | 3.30 mm | 0.1299 in | Cutting-tap reference · 75% theoretical full thread | Cross-checked, consistent | Haas 2024Guhring |
| M4.5 × 0.75 | 0.75 mm | 3.70 mm Manufacturer reference difference: Haas 2024 lists 3.70 mm (approximately 0.1457 in); Guhring lists #25 for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 0.1457 in | Cutting-tap reference · 75% theoretical full thread | Difference disclosed | Haas 2024Guhring |
| M5 × 0.80 | 0.80 mm | 4.20 mm | 0.1654 in | Cutting-tap reference · 75% theoretical full thread | Cross-checked, consistent | Haas 2024Guhring |
| M6 × 1.00 | 1.00 mm | 5.00 mm | 0.1969 in | Cutting-tap reference · 75% theoretical full thread | Cross-checked, consistent | Haas 2024Guhring |
| M6 × 0.75 | 0.75 mm | 5.25 mm | 0.2067 in | Cutting-tap reference · 75% theoretical full thread | Cross-checked, consistent | Haas 2024Guhring |
| M7 × 1.00 | 1.00 mm | 6.00 mm | 0.2362 in | Cutting-tap reference · 75% theoretical full thread | Cross-checked, consistent | Haas 2024Guhring |
| M8 × 1.25 | 1.25 mm | 6.75 mm Manufacturer reference difference: Haas 2024 lists 6.75 mm (approximately 0.2657 in); Guhring lists Letter H (0.2660 in) for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 0.2657 in | Cutting-tap reference · 75% theoretical full thread | Difference disclosed | Haas 2024Guhring |
| M8 × 1.00 | 1.00 mm | 7.00 mm | 0.2756 in | Cutting-tap reference · 75% theoretical full thread | Cross-checked, consistent | Haas 2024Guhring |
| M10 × 1.50 | 1.50 mm | 8.50 mm | 0.3346 in | Cutting-tap reference · 75% theoretical full thread | Cross-checked, consistent | Haas 2024Guhring |
| M10 × 1.25 | 1.25 mm | 8.75 mm Manufacturer reference difference: Haas 2024 lists 8.75 mm (approximately 0.3445 in); Guhring lists 11/32 in for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 0.3445 in | Cutting-tap reference · 75% theoretical full thread | Difference disclosed | Haas 2024Guhring |
| M12 × 1.75 | 1.75 mm | 10.20 mm Manufacturer reference difference: Haas 2024 lists 10.20 mm (approximately 0.4016 in); Guhring lists 10.30 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 0.4016 in | Cutting-tap reference · 75% theoretical full thread | Difference disclosed | Haas 2024Guhring |
| M12 × 1.25 | 1.25 mm | 10.80 mm | 0.4252 in | Cutting-tap reference · 75% theoretical full thread | Secondary comparison unavailable | Haas 2024 |
| M14 × 2.00 | 2.00 mm | 12.00 mm | 0.4724 in | Cutting-tap reference · 75% theoretical full thread | Cross-checked, consistent | Haas 2024Guhring |
| M14 × 1.50 | 1.50 mm | 12.50 mm | 0.4921 in | Cutting-tap reference · 75% theoretical full thread | Cross-checked, consistent | Haas 2024Guhring |
| M16 × 2.00 | 2.00 mm | 14.00 mm | 0.5512 in | Cutting-tap reference · 75% theoretical full thread | Cross-checked, consistent | Haas 2024Guhring |
| M16 × 1.50 | 1.50 mm | 14.50 mm | 0.5709 in | Cutting-tap reference · 75% theoretical full thread | Cross-checked, consistent | Haas 2024Guhring |
| M18 × 2.50 | 2.50 mm | 15.50 mm | 0.6102 in | Cutting-tap reference · 75% theoretical full thread | Cross-checked, consistent | Haas 2024Guhring |
| M18 × 1.50 | 1.50 mm | 16.50 mm | 0.6496 in | Cutting-tap reference · 75% theoretical full thread | Cross-checked, consistent | Haas 2024Guhring |
| M20 × 2.50 | 2.50 mm | 17.50 mm | 0.6890 in | Cutting-tap reference · 75% theoretical full thread | Cross-checked, consistent | Haas 2024Guhring |
| M20 × 1.50 | 1.50 mm | 18.50 mm | 0.7283 in | Cutting-tap reference · 75% theoretical full thread | Cross-checked, consistent | Haas 2024Guhring |
UNC Tap Drill Chart
Common Unified National Coarse sizes.
| Thread size | Pitch / TPI | Tap drill | Approx. converted | Applicability | Verification | Source |
|---|---|---|---|---|---|---|
| 2-56 | 56 TPI | 0.0686 in Manufacturer reference difference: OSG 2024 lists 0.0686 in (approximately 1.7424 mm); Guhring lists 1.73 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 1.7424 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
| 4-40 | 40 TPI | 0.0876 in Manufacturer reference difference: OSG 2024 lists 0.0876 in (approximately 2.2250 mm); Guhring lists 2.20 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 2.2250 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
| 6-32 | 32 TPI | 0.1076 in Manufacturer reference difference: OSG 2024 lists 0.1076 in (approximately 2.7330 mm); Guhring lists #36 for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 2.7330 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
| 8-32 | 32 TPI | 0.1336 in Manufacturer reference difference: OSG 2024 lists 0.1336 in (approximately 3.3934 mm); Guhring lists 3.40 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 3.3934 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
| 10-24 | 24 TPI | 0.1494 in Manufacturer reference difference: OSG 2024 lists 0.1494 in (approximately 3.7948 mm); Guhring lists #25 for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 3.7948 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
| 1/4-20 | 20 TPI | 0.2013 in Manufacturer reference difference: OSG 2024 lists 0.2013 in (approximately 5.1130 mm); Guhring lists #7 for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 5.1130 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
| 5/16-18 | 18 TPI | 0.2584 in Manufacturer reference difference: OSG 2024 lists 0.2584 in (approximately 6.5634 mm); Guhring lists Letter F for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 6.5634 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
| 3/8-16 | 16 TPI | 0.3141 in Manufacturer reference difference: OSG 2024 lists 0.3141 in (approximately 7.9781 mm); Guhring lists 5/16 in for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 7.9781 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
| 7/16-14 | 14 TPI | 0.3679 in Manufacturer reference difference: OSG 2024 lists 0.3679 in (approximately 9.3447 mm); Guhring lists Letter U for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 9.3447 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
| 1/2-13 | 13 TPI | 0.4251 in Manufacturer reference difference: OSG 2024 lists 0.4251 in (approximately 10.7975 mm); Guhring lists 27/64 in for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 10.7975 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
| 9/16-12 | 12 TPI | 0.4813 in Manufacturer reference difference: OSG 2024 lists 0.4813 in (approximately 12.2250 mm); Guhring lists 12.20 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 12.2250 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
| 5/8-11 | 11 TPI | 0.5364 in Manufacturer reference difference: OSG 2024 lists 0.5364 in (approximately 13.6246 mm); Guhring lists 13.60 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 13.6246 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
| 3/4-10 | 10 TPI | 0.6526 in Manufacturer reference difference: OSG 2024 lists 0.6526 in (approximately 16.5760 mm); Guhring lists 16.50 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 16.5760 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
| 7/8-9 | 9 TPI | 0.7668 in Manufacturer reference difference: OSG 2024 lists 0.7668 in (approximately 19.4767 mm); Guhring lists 19.50 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 19.4767 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
| 1-8 | 8 TPI | 0.8782 in Manufacturer reference difference: OSG 2024 lists 0.8782 in (approximately 22.3063 mm); Guhring lists 22.25 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 22.3063 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
UNF Tap Drill Chart
Common Unified National Fine sizes.
| Thread size | Pitch / TPI | Tap drill | Approx. converted | Applicability | Verification | Source |
|---|---|---|---|---|---|---|
| 0-80 | 80 TPI | 0.0478 in Manufacturer reference difference: OSG 2024 lists 0.0478 in (approximately 1.2141 mm); Guhring lists 1.20 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 1.2141 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
| 1-72 | 72 TPI | 0.0595 in | 1.5113 mm | Cut taps · 75% theoretical full thread | Cross-checked, consistent | OSG 2024Guhring |
| 2-64 | 64 TPI | 0.0708 in Manufacturer reference difference: OSG 2024 lists 0.0708 in (approximately 1.7983 mm); Guhring lists 1.80 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 1.7983 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
| 3-56 | 56 TPI | 0.0816 in Manufacturer reference difference: OSG 2024 lists 0.0816 in (approximately 2.0726 mm); Guhring lists #46 for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 2.0726 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
| 4-48 | 48 TPI | 0.0917 in Manufacturer reference difference: OSG 2024 lists 0.0917 in (approximately 2.3292 mm); Guhring lists 2.32 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 2.3292 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
| 5-44 | 44 TPI | 0.1029 in Manufacturer reference difference: OSG 2024 lists 0.1029 in (approximately 2.6137 mm); Guhring lists 2.60 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 2.6137 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
| 6-40 | 40 TPI | 0.1136 in Manufacturer reference difference: OSG 2024 lists 0.1136 in (approximately 2.8854 mm); Guhring lists #33 for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 2.8854 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
| 8-36 | 36 TPI | 0.1369 in Manufacturer reference difference: OSG 2024 lists 0.1369 in (approximately 3.4773 mm); Guhring lists #29 for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 3.4773 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
| 10-32 | 32 TPI | 0.1596 in Manufacturer reference difference: OSG 2024 lists 0.1596 in (approximately 4.0538 mm); Guhring lists #21 for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 4.0538 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
| 12-28 | 28 TPI | 0.1812 in Manufacturer reference difference: OSG 2024 lists 0.1812 in (approximately 4.6025 mm); Guhring lists 4.60 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 4.6025 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
| 1/4-28 | 28 TPI | 0.2152 in Manufacturer reference difference: OSG 2024 lists 0.2152 in (approximately 5.4661 mm); Guhring lists 5.45 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 5.4661 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
| 5/16-24 | 24 TPI | 0.2719 in | 6.9063 mm | Cut taps · 75% theoretical full thread | Cross-checked, consistent | OSG 2024Guhring |
| 3/8-24 | 24 TPI | 0.3344 in Manufacturer reference difference: OSG 2024 lists 0.3344 in (approximately 8.4938 mm); Guhring lists 8.50 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 8.4938 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
| 7/16-20 | 20 TPI | 0.3888 in Manufacturer reference difference: OSG 2024 lists 0.3888 in (approximately 9.8755 mm); Guhring lists 9.95 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 9.8755 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
| 1/2-20 | 20 TPI | 0.4513 in Manufacturer reference difference: OSG 2024 lists 0.4513 in (approximately 11.4630 mm); Guhring lists 11.40 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 11.4630 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
| 9/16-18 | 18 TPI | 0.5084 in Manufacturer reference difference: OSG 2024 lists 0.5084 in (approximately 12.9134 mm); Guhring lists 12.90 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 12.9134 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
| 5/8-18 | 18 TPI | 0.5709 in | 14.5009 mm | Cut taps · 75% theoretical full thread | Cross-checked, consistent | OSG 2024Guhring |
| 3/4-16 | 16 TPI | 0.6891 in Manufacturer reference difference: OSG 2024 lists 0.6891 in (approximately 17.5031 mm); Guhring lists 17.50 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 17.5031 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
| 7/8-14 | 14 TPI | 0.8054 in Manufacturer reference difference: OSG 2024 lists 0.8054 in (approximately 20.4572 mm); Guhring lists 20.40 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 20.4572 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
| 1-12 | 12 TPI | 0.9188 in Manufacturer reference difference: OSG 2024 lists 0.9188 in (approximately 23.3375 mm); Guhring lists 23.30 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill. | 23.3375 mm | Cut taps · 75% theoretical full thread | Difference disclosed | OSG 2024Guhring |
Review 37 manufacturer reference differences
- M2.5 × 0.45:
Manufacturer reference difference: Haas 2024 lists 2.05 mm (approximately 0.0807 in); Guhring lists #46 for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
Haas 2024Guhring - M4.5 × 0.75:
Manufacturer reference difference: Haas 2024 lists 3.70 mm (approximately 0.1457 in); Guhring lists #25 for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
Haas 2024Guhring - M8 × 1.25:
Manufacturer reference difference: Haas 2024 lists 6.75 mm (approximately 0.2657 in); Guhring lists Letter H (0.2660 in) for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
Haas 2024Guhring - M10 × 1.25:
Manufacturer reference difference: Haas 2024 lists 8.75 mm (approximately 0.3445 in); Guhring lists 11/32 in for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
Haas 2024Guhring - M12 × 1.75:
Manufacturer reference difference: Haas 2024 lists 10.20 mm (approximately 0.4016 in); Guhring lists 10.30 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
Haas 2024Guhring - 2-56:
Manufacturer reference difference: OSG 2024 lists 0.0686 in (approximately 1.7424 mm); Guhring lists 1.73 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring - 4-40:
Manufacturer reference difference: OSG 2024 lists 0.0876 in (approximately 2.2250 mm); Guhring lists 2.20 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring - 6-32:
Manufacturer reference difference: OSG 2024 lists 0.1076 in (approximately 2.7330 mm); Guhring lists #36 for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring - 8-32:
Manufacturer reference difference: OSG 2024 lists 0.1336 in (approximately 3.3934 mm); Guhring lists 3.40 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring - 10-24:
Manufacturer reference difference: OSG 2024 lists 0.1494 in (approximately 3.7948 mm); Guhring lists #25 for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring - 1/4-20:
Manufacturer reference difference: OSG 2024 lists 0.2013 in (approximately 5.1130 mm); Guhring lists #7 for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring - 5/16-18:
Manufacturer reference difference: OSG 2024 lists 0.2584 in (approximately 6.5634 mm); Guhring lists Letter F for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring - 3/8-16:
Manufacturer reference difference: OSG 2024 lists 0.3141 in (approximately 7.9781 mm); Guhring lists 5/16 in for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring - 7/16-14:
Manufacturer reference difference: OSG 2024 lists 0.3679 in (approximately 9.3447 mm); Guhring lists Letter U for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring - 1/2-13:
Manufacturer reference difference: OSG 2024 lists 0.4251 in (approximately 10.7975 mm); Guhring lists 27/64 in for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring - 9/16-12:
Manufacturer reference difference: OSG 2024 lists 0.4813 in (approximately 12.2250 mm); Guhring lists 12.20 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring - 5/8-11:
Manufacturer reference difference: OSG 2024 lists 0.5364 in (approximately 13.6246 mm); Guhring lists 13.60 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring - 3/4-10:
Manufacturer reference difference: OSG 2024 lists 0.6526 in (approximately 16.5760 mm); Guhring lists 16.50 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring - 7/8-9:
Manufacturer reference difference: OSG 2024 lists 0.7668 in (approximately 19.4767 mm); Guhring lists 19.50 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring - 1-8:
Manufacturer reference difference: OSG 2024 lists 0.8782 in (approximately 22.3063 mm); Guhring lists 22.25 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring - 0-80:
Manufacturer reference difference: OSG 2024 lists 0.0478 in (approximately 1.2141 mm); Guhring lists 1.20 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring - 2-64:
Manufacturer reference difference: OSG 2024 lists 0.0708 in (approximately 1.7983 mm); Guhring lists 1.80 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring - 3-56:
Manufacturer reference difference: OSG 2024 lists 0.0816 in (approximately 2.0726 mm); Guhring lists #46 for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring - 4-48:
Manufacturer reference difference: OSG 2024 lists 0.0917 in (approximately 2.3292 mm); Guhring lists 2.32 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring - 5-44:
Manufacturer reference difference: OSG 2024 lists 0.1029 in (approximately 2.6137 mm); Guhring lists 2.60 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring - 6-40:
Manufacturer reference difference: OSG 2024 lists 0.1136 in (approximately 2.8854 mm); Guhring lists #33 for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring - 8-36:
Manufacturer reference difference: OSG 2024 lists 0.1369 in (approximately 3.4773 mm); Guhring lists #29 for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring - 10-32:
Manufacturer reference difference: OSG 2024 lists 0.1596 in (approximately 4.0538 mm); Guhring lists #21 for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring - 12-28:
Manufacturer reference difference: OSG 2024 lists 0.1812 in (approximately 4.6025 mm); Guhring lists 4.60 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring - 1/4-28:
Manufacturer reference difference: OSG 2024 lists 0.2152 in (approximately 5.4661 mm); Guhring lists 5.45 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring - 3/8-24:
Manufacturer reference difference: OSG 2024 lists 0.3344 in (approximately 8.4938 mm); Guhring lists 8.50 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring - 7/16-20:
Manufacturer reference difference: OSG 2024 lists 0.3888 in (approximately 9.8755 mm); Guhring lists 9.95 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring - 1/2-20:
Manufacturer reference difference: OSG 2024 lists 0.4513 in (approximately 11.4630 mm); Guhring lists 11.40 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring - 9/16-18:
Manufacturer reference difference: OSG 2024 lists 0.5084 in (approximately 12.9134 mm); Guhring lists 12.90 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring - 3/4-16:
Manufacturer reference difference: OSG 2024 lists 0.6891 in (approximately 17.5031 mm); Guhring lists 17.50 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring - 7/8-14:
Manufacturer reference difference: OSG 2024 lists 0.8054 in (approximately 20.4572 mm); Guhring lists 20.40 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring - 1-12:
Manufacturer reference difference: OSG 2024 lists 0.9188 in (approximately 23.3375 mm); Guhring lists 23.30 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
OSG 2024Guhring
Using the reference
How to Read the Chart
Match the thread designation and pitch or TPI, then read the tap drill and its unit. A metric input without pitch returns the listed coarse pitch and marks that default explicitly.
- Metric pitch is the axial distance between thread crests in millimeters.
- UNC and UNF pitch is shown as threads per inch (TPI).
- “Approx. converted” is a unit conversion of the listed diameter, not a separately specified standard drill size.
- Thread percentage is theoretical. Drilling runout and process variation affect the actual thread percentage.
Tap type matters
Cutting Tap vs Forming Tap
This chart is scoped to cutting taps. Forming taps displace material and use different pre-hole guidance; their values are not included here.
Do not apply a cutting-tap drill value to a forming tap. Guhring publishes separate cut-tap and form-tap target thread-percentage tables, illustrating why the tool type must be confirmed before selecting a drill.
Manufacturer references
Published Source Differences
Different official charts may list different pilot drill sizes. Source values remain separate and are not averaged. The chart rows and lookup disclose each reviewed difference.
- 1/4-28 UNF: OSG lists 0.2152 in (approximately 5.466 mm), while Guhring lists 5.45 mm for its 75% theoretical cut-tap reference. Values are not identical. Confirm the applicable manufacturer guidance before selecting a drill.
- M2.5 × 0.45: Haas lists 2.05 mm; Guhring lists a #46 drill designation in its 75% cut-tap column.
- M4.5 × 0.75: Haas lists 3.70 mm. Guhring’s 75% cut-tap row identifies a #25 drill, about 3.80 mm.
- M10 × 1.25: Haas lists 8.75 mm; Guhring’s 75% reference lists an 11/32 in drill (about 8.73 mm).
- M12 × 1.75: Haas lists 10.20 mm; Guhring lists 10.30 mm at its 75% cut-tap target.
- 1/4-20 UNC: OSG lists 0.2013 in; Guhring lists a #7 drill designation for its 75% cut-tap target (0.2010 in in Guhring’s decimal drill-size chart).
- 1/2-13 UNC: OSG lists 0.4251 in; Guhring lists a 27/64 in drill for its 75% cut-tap target (approximately 0.4219 in).
These are recorded as published differences. No universal cause or single correct value is inferred. Tap percentage values are theoretical references, not a claim that a specific nominal drill is universally suitable. Consult the current documentation for the selected tap and application. See the Haas guide, OSG chart, and Guhring chart.
FAQ
What does a result for M8 mean when I enter only M8?
The lookup selects the M8 × 1.25 coarse-pitch row in this dataset and labels it as the default. Enter a complete designation such as M8x1 to select another listed pitch.
Is the listed tap drill size the only correct choice?
No. These are source-backed reference values at a stated theoretical thread percentage. Tap maker guidance, fit class, material, and process conditions can change the appropriate drill size.
Can I use these sizes with forming taps?
No. This chart is limited to cutting taps. Forming taps require separate drill-size guidance, which is not included in these tables.
Why might two manufacturer charts show different drill sizes?
Published references can differ, even at a stated 75% thread target. See the Published Source Differences section and review the source links for each chart. This page keeps source values distinct rather than averaging them.
Source documentation
Technical References
Metric and inch values are attributed to their source records. Guhring’s technical material is also used to explain cut versus forming tap guidance.
- Haas Machinist’s CNC Reference Guide (2024)
Metric tap sizes and drill diameters; the guide identifies its metric table as based on 75% full thread.
- OSG Tap Drill Size & Pitch Diameter Limits, Vol. 3 (2024)
Fractional cut-tap chart with 80%, 75%, 70%, 65%, and 60% thread columns. This page displays the 75% column.
- Guhring Tap Drill Sizes
Manufacturer reference with distinct cutting-tap and forming-tap sections and 55%, 65%, and 75% theoretical thread targets.
- Guhring Tapping Technical References
Index of manufacturer tapping references, including separate metric and UNC/UNF drill-size tables.