These tapping drills are recommended for use with steel only and will give approximately 75% depth of thread. Deviations from these drill sizes will be necessary, depending on the nature of the material and requirements of the finished work.
| Diam. | Tapping | Clearance |
| 0 | 5.10mm | 6.20mm |
| 1 | 4.50mm | 5.50mm |
| 2 | 5/32" | 4.90mm |
| 3 | 3.50mm | 4.20mm |
| 4 | 3.00mm | 3.70mm |
| 5 | 2.70mm | 3.30mm |
| 6 | 3/32" | 2.90mm |
| 7 | 2.10mm | 2.60mm |
| 8 | 1.80mm | 2.30mm |
| 9 | 1.50mm | 2.00mm |
| 10 | 1.40mm | 1.80mm |
| 11 | 3/64" | 1.60mm |
| 12 | 1.05mm | 1.40mm |
| |B.A.|B.S. FINE|B.S. WHITWORTH|UNIFIED|I.S.O. METRIC COARSE|I.S.O. METRIC FINE| |
| Diam. | Tapping | Clearance |
| 3/16" | 4.00mm | 4.90mm |
| 7/32" | 4.70mm | 5.70mm |
| 1/4" | 5.40mm | 6.50mm |
| 9/32" | 6.20mm | 7.40mm |
| 5/16" | 6.90mm | 8.20mm |
| 3/8" | 21/64" | 9.80mm |
| 7/16" | 9.80mm | 29/64" |
| 1/2" | 7/16" | 33/64" |
| 9/16" | 1/2" | 37/64" |
| 5/8" | 9/16" | 41/64" |
| 11/16" | 5/8" | 45/64" |
| 3/4" | 43/64" | 49/64" |
| 13/16" | 47/64" | 53/64" |
| 7/8" | 51/64" | 57/64" |
| 1" | 29/32" | 1&1/64" |
| |B.A.|B.S. FINE|B.S. WHITWORTH|UNIFIED|I.S.O. METRIC COARSE|I.S.O. METRIC FINE| |
| Diam. | Tapping | Clearance |
| 1/16" | 3/64" | 1.70mm |
| 3/32" | 1.90mm | 2.50mm |
| 1/8" | 2.60mm | 3.30mm |
| 5/32" | 3.20mm | 4.10mm |
| 3/16" | 3.80mm | 4.90mm |
| 7/32" | 4.60mm | 5.70mm |
| 1/4" | 13/64" | 6.50mm |
| 5/16" | 6.60mm | 8.20mm |
| 3/8" | 8.00mm | 9.80mm |
| 7/16" | 9.30mm | 29/64" |
| 1/2" | 27/64" | 33/64" |
| 9/16" | 31/64" | 37/64" |
| 5/8" | 17/32" | 41/64" |
| 3/4" | 21/32" | 49/64" |
| 7/8" | 49/64" | 57/64" |
| 1" | 7/8" | 1&1/64" |
| |B.A.|B.S. FINE|B.S. WHITWORTH|UNIFIED|I.S.O. METRIC COARSE|I.S.O. METRIC FINE| |
| Diam. |
Tapping U.N.C. |
Tapping U.N.C. |
Clearance |
| 0 | - | 3/64" | 1/16" |
| 1 | 1.45mm | 1.50mm | 1.95mm |
| 2 | 1.70mm | 1.80mm | 2.25mm |
| 3 | 5/64" | 2.05mm | 2.60mm |
| 4 | 2.20mm | 2.30mm | 2.95mm |
| 5 | 2.55mm | 2.60mm | 3.30mm |
| 6 | 2.70mm | 2.90mm | 9/64" |
| 8 | 3.40mm | 3.50mm | 4.30mm |
| 10 | 3.80mm | 4.00mm | 4.90mm |
| 12 | 4.40mm | 4.60mm | 5.60mm |
| 1/4" | 13/64" | 5.40mm | 6.50mm |
| 5/16" | 6.50mm | 6.90mm | 8.20mm |
| 3/8" | 5/16" | 8.50mm | 9.80mm |
| 7/16" | 9.30mm | 25/64" | 29/64" |
| 1/2" | 27/64" | 29/64" | 33/64" |
| 9/16" | 31/64" | 13.00mm | 37/64" |
| 5/8" | 17/32" | 14.50mm | 41/64" |
| 3/4" | 16.50mm | 11/16" | 49/64" |
| 7/8" | 49/64" | 20.50mm | 57/64" |
| 1" | 7/8" | 23.50mm | 1&1/64" |
| |B.A.|B.S. FINE|B.S. WHITWORTH|UNIFIED|I.S.O. METRIC COARSE|I.S.O. METRIC FINE| |
| Diam. | Tapping | Clearance |
| M1.0 | 0.78mm | 1.1mm |
| M1.1 | 0.88mm | 1.2mm |
| M1.2 | 0.98mm | 1.3mm |
| M1.4 | 1.15mm | 1.5mm |
| M1.6 | 1.3mm | 1.7mm |
| M1.8 | 1.5mm | 1.9mm |
| M2.0 | 1.65mm | 2.2mm |
| M2.2 | 1.8mm | 2.4mm |
| M2.5 | 2.1mm | 2.7mm |
| M3.0 | 2.55mm | 3.2mm |
| M3.5 | 2.95mm | 3.7mm |
| M4.0 | 3.4mm | 4.3mm |
| M4.5 | 3.8mm | 4.8mm |
| M5 | 4.3mm | 5.3mm |
| M6 | 5.1mm | 6.4mm |
| M7 | 6.1mm | 7.4mm |
| M8 | 6.9mm | 8.4mm |
| M9 | 7.9mm | 9.4mm |
| M10 | 8.6mm | 10.5mm |
| M11 | 9.6mm | 11.5mm |
| M12 | 10.4mm | 13.0mm |
| M14 | 12.2mm | 15.0mm |
| M16 | 14.25mm | 17.0mm |
| M18 | 15.75mm | 19.0mm |
| M20 | 17.75mm | 21.0mm |
| M22 | 19.75mm | 23.0mm |
| M24 | 21.25mm | 25.0mm |
| M27 | 24.25mm | 28.0mm |
| M30 | 27.0mm | 31.0mm |
| M33 | 30.0mm | 34.0mm |
| M36 | 32.5mm | 37.0mm |
| M39 | 35.5mm | 40.0mm |
| M42 | 38.0mm | 43.0mm |
| M45 | 41.0mm | 46.0mm |
| M56 | 51.0mm | 58.0mm |
| M60 | 55.0mm | 62.0mm |
| M64 | 58.0mm | 66.0mm |
| M68 | 62.0mm | 70.0mm |
| |B.A.|B.S. FINE|B.S. WHITWORTH|UNIFIED|I.S.O. METRIC COARSE|I.S.O. METRIC FINE| |
| Tapping | Clearance |
|
There are also ISO Metric Fine Pitch threads but as these are many and varied,
it is suggested that the tapping drill is derived as follows:
Tapping Drill = Outside diam. - Pitch |
Clearance Drills as per table for ISO Metric Coarse |
| |B.A.|B.S. FINE|B.S. WHITWORTH|UNIFIED|I.S.O. METRIC COARSE|I.S.O. METRIC FINE| |