Tap drills
10-32 tap drill size
The tap drill for 10-32 is #21, which is 0.1590 inches or 4.04 mm. That leaves about 76 percent thread engagement.
10-32 tap drill, clearance and engagement
| Series | UNF (fine) |
| Major diameter | 0.1900 in (4.83 mm) |
| Threads per inch | 32 |
| Tap drill | #21 (0.1590 in / 4.04 mm) |
| Thread engagement | 76% |
| Drill for 75% thread | 0.1596 in |
| Clearance, close fit | #11 (0.1910 in) |
| Nearest metric drill | 4 mm (0.1575 in) |
What 10-32 is used for
The fine-thread partner to 10-24, and the standard rack-mount thread in EIA-310 equipment racks. Also common in avionics, electronics chassis and anywhere vibration resistance matters.
If you do not have that drill
5/32 at 0.1562 is 0.0028 under a number 21 and pushes engagement to about 89 percent, which tapping torque will show you. Prefer the number 21.
How to tap a 10-32 thread
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Drill the hole
Use a #21 drill, 0.1590 inches or 4.04 mm. Drill square to the surface and clear the swarf on deep holes.
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Start the tap square
Start with a taper tap and check it is square in both axes within the first two turns. A tap started crooked will cut a crooked thread all the way down and cannot be corrected.
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Cut and break the chip
Turn forward about half a turn, then back a quarter turn to break the chip. Use cutting fluid on steel and stainless; aluminium and brass usually need none, though a wax stick helps in aluminium.
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Check the fit
Run the mating fastener in by hand. It should turn freely without side play. If it binds, the hole was undersized or the tap wandered.
Common questions
What size drill do I need for a 10-32 tap?
- The tap drill for 10-32 is #21, which is 0.1590 inches or 4.04 mm. That leaves about 76 percent thread engagement. 5/32 at 0.1562 is 0.0028 under a number 21 and pushes engagement to about 89 percent, which tapping torque will show you. Prefer the number 21.
What is the clearance hole for a 10-32 bolt?
- #11, which is 0.1910 inches. That is a close fit. A normal fit is one drill size larger and a loose fit two, and the looser classes are the sensible choice when the parts have to line up without reaming.
How is the 10-32 tap drill worked out?
- Take the major diameter and subtract the engagement fraction times 1.299 divided by threads per inch: 0.1900 minus 0.75 times 1.299 divided by 32 gives 0.1596 inches. The nearest standard drill is #21 at 0.1590 inches.
Can I use a metric drill for a 10-32 tap?
- The closest standard metric drill is 4 mm, which is 0.1575 inches against 0.1590 for #21. That changes engagement to about 80 percent, so check that figure is acceptable for your material before substituting.