Drill Sizes for Cut Tapping
Metric System
Notes:
1. This chart is supplied as a recommendation only. Actual sizes may vary depending on application and the
material being tapped. Other thread and hole sizes are available upon request.
2. For aluminum or other soft materials a hole minor diameter on the low side of the suggested range is
recommended. For harder materials a hole minor diameter on the high side of the suggested range is
recommended.
3. These recommendations are for cutting with regular preload-locking threading taps.
4. Preload-locking threads can be applied to threading tools in sizes from 0.30 mm.
Metric Hole Minor Hole Minor Drill Metric Hole Minor Hole Minor Drill
Thread Dia. Min Dia. Max Size* Thread Dia. Min Dia. Max Size*
Size (mm) (mm) Size (mm) (mm)
M2.5 x 0.45 2.210 2.261 #43 M14.0 x 2.00 12.319 12.700 31/64
M3.0 x 0.50 2.667 2.743 #36 M16.0 x 1.50 14.732 15.037 15 mm
M3.5 x 0.60 3.099 3.200 1/8 M16.0 x 2.00 14.300 14.707 9/16
M4.0 x 0.70 3.556 3.632 #28 M18.0 x 1.50 16.739 17.018 17 mm
M4.5 x 0.75 4.013 4.115 #21 M18.0 x 2.50 15.875 16.383 5/8
M5.0 x 0.80 4.318 4.470 11/64 M20.0 x 1.50 18.745 19.025 19 mm
M6.0 x 1.00 5.156 5.359 #5 M20.0 x 2.50 17.882 18.364 23/32
M7.0 x 1.00 6.147 6.350 C M22.0 x 1.50 20.726 21.031 21 mm
M8.0 x 1.00 7.163 7.341 9/32 M22.0 x 2.50 19.888 20.371 20 mm
M8.0 x 1.25 6.934 7.188 J M24.0 x 3.00 21.463 22.047 55/64
M9.0 x 1.25 7.950 8.179 8 mm M27.0 x 3.00 24.460 25.044 31/32
M10.0 x 1.25 8.941 9.195 T M28.0 x 1.50 26.746 27.026 1 1/16
M10.0 x 1.50 8.738 9.017 S M30.0 x 2.00 28.321 28.702 28.5 mm
M11.0 x 1.50 9.728 10.033 W M30.0 x 3.50 27.051 27.737 1 5/64
M12.0 x 1.25 10.947 11.176 11 mm M33.0 x 2.00 31.318 31.699 1 15/64
M12.0 x 1.75 10.516 10.871 27/64 M33.0 x 3.50 30.048 30.734 1 3/16
M14.0 x 1.25 12.954 13.183 33/64 M36.0 x 4.00 32.614 33.401 1 5/16
M14.0 x 1.50 12.725 13.030 13 mm M39.0 x 4.00 35.611 36.398 1 13/32
* Note: Drill size callouts were determined to best fit the hole minor diameter range.
Drill Sizes for Cut Tapping
Fractional System
Notes:
1. This chart is supplied as a recommendation only. Actual sizes may vary depending on application and the
material being tapped. Other thread and hole sizes are available upon request.
2. For aluminum or other soft materials a hole minor diameter on the low side of the suggested range is
recommended. For harder materials a hole minor diameter on the high side of the suggested range is
recommended.
3. These recommendations are for cutting with regular preload-locking threading taps.
4. Preload-locking threads can be applied to threading tools in sizes from #0000-160 Inch.
Fractional Hole Minor Hole Minor Drill Fractional Hole Minor Hole Minor Drill
Thread Diameter Diameter Size* Thread Size Diameter Diameter Size*
Size Min. Max. Min. Max.
0 – 80 0.0520 0.0540 #55 7/16 – 20 0.3950 0.4050 X
2 – 56 0.0740 0.0770 #48 1/2 – 13 0.4350 0.4500 7/16
2 – 64 0.0760 0.0780 1.95mm 1/2 – 20 0.4580 0.4680 11.75mm
3 – 48 0.0850 0.0880 #44 9/16 – 12 0.4920 0.5080 1/2
3 – 56 0.0870 0.0900 #43 9/16 – 18 0.5160 0.5260 33/64
4 – 40 0.0960 0.0990 #41 5/8 – 11 0.5480 0.5660 14 mm
4 – 48 0.0980 0.1010 #40 5/8 – 18 0.5780 0.5890 37/64
5 – 40 0.1090 0.1120 7/64 3/4 – 10 0.6660 0.6850 43/64
5 – 44 0.1100 0.1130 #35 3/4 – 16 0.6970 0.7090 45/64
6 – 32 0.1120 0.1180 #33 7/8 – 9 0.7810 0.8030 25/32
6 – 40 0.1220 0.1250 1/8 7/8 – 14 0.8150 0.8290 21 mm
8 – 32 0.1380 0.1440 #28 1” – 8 0.8940 0.9190 29/32
8 – 36 0.1460 0.1500 #26 1” – 12 0.9300 0.9460 15/16
10 – 24 0.1550 0.1630 #21 1” – 14 0.9400 0.9540 24 mm
10 – 32 0.1640 0.1700 #19 1 1/8-7 1.0040 1.0320 1 1/64
12 – 24 0.1810 0.1890 #13 1 1/8-12 1.0550 1.0710 1 1/16
12 – 28 0.1860 0.1930 #12 1 1/4-7 1.1290 1.1570 1 9/64
1/4 - 20 0.2080 0.2180 #4 1 1/4-12 1.1800 1.1960 1 3/16
1/4 - 28 0.2200 0.2270 #2 1 3/8-6 1.2340 1.2670 1 1/4
5/16 – 18 0.2660 0.2760 H 1 3/8-12 1.3050 1.3210 1 5/16
5/16 – 24 0.2770 0.2850 J 1 1/2-6 1.3590 1.3920 1 3/8
3/8 – 16 0.3220 0.3340 P 1 1/2-12 1.4300 1.4460 1 7/16
3/8 – 24 0.3400 0.3480 11/32
7/16 - 14 0.3770 0.3910 V
* Note: Drill size callouts were determined to best fit the hole minor diameter range.
Hole Sizes for Cold Form Tapping
Metric System
IMPORTANT NOTES ON SPIRALOCK PRETAP HOLE SIZES
Determining Drill Size
Finding the correct drill size for a Spiralock tap may be a “Cut and Try” process.
Not all drills are alike and therefore the pretap holes produced by different drills may be vastly different.
What matters is the actual pretap hole size, how consistently this hole size is maintained, and finally,
the after-tap thread percentage or minor diameter. To get good results, you must know the actual hole
size and not just the drill size!
Thin wall parts may expand during tapping and produce oversize after-tap minor diameters.
Diecast parts may contain porosity, which may cause oversize holes due to shrinkage.
After tapping, thread minor diameter should check within Spiralock recommended minor diameter
sizes.
Suggested Procedure for Using Spiralock Tap
1. Test drill a part and measure the pretap hole size.
2. Test tap the part. Check pitch diameter with GO and NOT-GO gages. Check the thread percentage or
minor diameter against the customer requirement.
3. Establish a maximum condition for the pretap hole size and monitor this frequently during the
production tap run.
Pre-tap Hole Diameter Pre-tap Hole Diameter
Metric Cold-Form Cold-Form Metric Cold-Form Cold-Form
Thread Size Drill Dia. Drill Dia. Thread Size Drill Dia. Drill Dia.
Min. (mm) Max. (mm) Min. (mm) Max. (mm)
M2.5 x 0.45 2.352 2.380 M14.0 x 2.00 13.160 13.350
M3.0 x 0.50 2.835 2.865 M16.0 x 1.50 15.367 15.519
M3.5 x 0.60 3.302 3.335 M16.0 x 2.00 15.151 15.354
M4.0 x 0.70 3.769 3.805 M18.0 x 1.50 17.369 17.508
M4.5 x 0.75 4.257 4.308 M18.0 x 2.50 16.937 17.191
M5.0 x 0.80 4.658 4.735 M20.0 x 1.50 19.373 19.512
M6.0 x 1.00 5.578 5.679 M20.0 x 2.50 18.857 18.908
M7.0 x 1.00 6.574 6.675 M22.0 x 1.50 21.364 21.516
M8.0 x 1.00 7.582 7.671 M22.0 x 2.50 20.945 21.186
M8.0 x 1.25 7.468 7.595 M24.0 x 3.00 22.731 23.023
M9.0 x 1.25 8.478 8.590 M27.0 x 3.00 25.730 26.022
M10.0 x 1.25 9.472 9.599 M28.0 x 1.50 27.374 27.513
M10.0 x 1.50 9.370 9.510 M30.0 x 2.00 29.162 29.352
M11.0 x 1.50 10.363 10.516 M30.0 x 3.50 28.527 28.870
M12.0 x 1.25 11.474 11.588 M33.0 x 2.00 32.159 32.349
M12.0 x 1.75 11.257 11.435 M33.0 x 3.50 31.524 31.867
M14.0 x 1.25 13.477 13.592 M36.0 x 4.00 34.308 34.702
M14.0 x 1.50 13.363 13.515 M39.0 x 4.00 37.341 37.699
Hole Sizes for Cold Form Tapping
Fractional System
IMPORTANT NOTES ON SPIRALOCK PRETAP HOLE SIZES
Determining Drill Size
Finding the correct drill size for a Spiralock tap may be a “Cut and Try” process.
Not all drills are alike and therefore the pretap holes produced by different drills may be vastly different.
What matters is the actual pretap hole size, how consistently this hole size is maintained, and finally,
the after-tap thread percentage or minor diameter. To get good results, you must know the actual hole
size and not just the drill size!
Thin wall parts may expand during tapping and produce oversize after-tap minor diameters.
Diecast parts may contain porosity, which may cause oversize holes due to shrinkage.
After tapping, thread minor diameter should check within Spiralock recommended minor diameter
sizes.
Suggested Procedure for Using Spiralock Tap
1. Test drill a part and measure the pretap hole size.
2. Test tap the part. Check pitch diameter with GO and NOT-GO gages. Check the thread percentage or
minor diameter against the customer requirement.
3. Establish a maximum condition for the pretap hole size and monitor this frequently during the
production tap run.
Pre-tap Hole Diameter Pre-tap Hole Diameter
Fractional Cold-Form Cold Form Fractional Cold-Form Cold Form
Thread Drill Dia. Drill Dia Thread Size Drill Dia. Drill Dia
Size Min. Max. Min. Max.
0 – 80 0.0559 0.0567 7/16 – 20 0.4164 0.4213
2 – 56 0.0801 0.0812 1/2 – 13 0.4675 0.4750
3 – 48 0.0921 0.0933 1/2 – 20 0.4789 0.4838
3 – 56 0.0931 0.0942 9/16 – 12 0.5273 0.5354
4 – 40 0.1038 0.1050 9/16 – 18 0.5390 0.5445
4 – 48 0.1051 0.1063 5/8 – 11 0.5866 0.5955
5 – 40 0.1168 0.1180 5/8 – 18 0.6015 0.6070
5 – 44 0.1175 0.1187 3/4 – 10 0.7078 0.7175
6 – 32 0.1248 0.1279 3/4 – 16 0.7236 0.7297
6 – 40 0.1298 0.1311 7/8 – 9 0.8281 0.8389
8 – 32 0.1508 0.1539 7/8 – 14 0.8448 0.8518
8 – 36 0.1548 0.1562 1” – 8 0.9472 0.9594
10 – 24 0.1724 0.1765 1” – 12 0.9648 0.9729
10 – 32 0.1768 0.1799 1” – 14 0.9698 0.9768
12 – 24 0.1984 0.2025 1 1/8-7 1.0647 1.0786
12 – 28 0.2009 0.2044 1 1/8-12 1.0898 1.0979
1/4 - 20 0.2289 0.2338 1 1/4-7 1.1897 1.2036
1/4 - 28 0.2349 0.2384 1 1/4-12 1.2148 1.2229
5/16 – 18 0.2890 0.2945 1 3/8-6 1.3046 1.3209
5/16 – 24 0.2949 0.2990 1 3/8-12 1.3398 1.3479
3/8 – 16 0.3486 0.3547 1 1/2-6 1.4296 1.4459
3/8 – 24 0.3574 0.3615 1 1/2-12 1.4648 1.4729
7/16 - 14 0.4073 0.4143
