# 8-32 tap drill size

URL: https://www.clove3d.com/tools/tap-drill/8-32/

Tap drill for 8-32 UNC: #29 (0.1360 in / 3.45 mm), about 69% thread.

## Thread specs

- Series: UNC
- Major diameter: 0.1640 in
- Pitch: 32 TPI
- Basic minor diameter: 0.1302 in

## Every drill that works (50-85% thread)

| Drill | % thread | in | mm | Good for |
|---|---|---|---|---|
| 3.6 mm | 55% | 0.1417 | 3.60 | deep holes only |
| 9/64" | 58% | 0.1406 | 3.57 | deep holes only |
| #28 | 58% | 0.1405 | 3.57 | deep holes only |
| 3.5 mm | 65% | 0.1378 | 3.50 | hard or tough metals |
| #29 (standard) | 69% | 0.1360 | 3.45 | hard or tough metals |
| 3.4 mm | 74% | 0.1339 | 3.40 | general use |
| 3.3 mm | 84% | 0.1299 | 3.30 | more torque, more broken taps |

## Clearance hole

- Close fit: #18 (0.1695 in / 4.31 mm)
- Free fit: #16 (0.1770 in / 4.50 mm)

## Counterbore (socket head cap screw)

- AMES: diameter 5/16" (0.3125 in), depth 0.1640 in

Countersink (flat head socket screw): 82 degrees to 0.3590 in across for a flush head.

## Heat-set insert hole (3D prints)

- Generic (Albany County): 0.1960 in

## Thread repair (Helicoil / STI drill)

- AMES: #17 (0.1730 in / 4.39 mm)
- MISUMI: 11/64" (0.1719 in / 4.37 mm)

## FAQ

Q: What size drill do I use for a 8-32 tap?
A: Use a #29 (0.1360 in / 3.45 mm) drill. It leaves about 69% thread, the standard for general-purpose tapping.

Q: What metric drill can I use for a 8-32 tap?
A: 3.4 mm (0.1339 in / 3.40 mm) is the closest, giving about 74% thread. Anything from about 65% to 80% thread taps well in most materials.

Q: What size clearance hole for a 8-32 screw?
A: #18 (0.1695") for a close fit, #16 (0.1770") for a free fit.

Q: What hole size for a 8-32 heat-set insert?
A: 0.1960" in the brands listed here. Check your insert's own listing; the hole is sized for that insert's knurl.

Q: What is the metric equivalent of 8-32?
A: M4 is the closest size (4.00 mm vs 4.17 mm major diameter). The pitches differ, so the screws and tapped holes are not interchangeable.

## Sources

- Engineers Edge: machinist screw thread tap drill chart (ANSI): https://engineersedge.com/tap_drill_chart.htm
- Penn MEDesign: tap drill chart: https://medesign.seas.upenn.edu/index.php/Guides.TapDrillChart
- Fractory: imperial clearance hole sizes: https://fractory.com/?p=21622
- AMES: counterbore hole dimensions, inch (Machinery's Handbook): https://amesweb.info/Screws/Counterbore-Hole-Dimensions-Chart.aspx
- SC Fastening: flat head socket cap screw spec, ASME B18.3 (PDF): https://scfastening.com/wp-content/uploads/2017/06/flatsocketspec.pdf
- Eugene Fastener: flat head socket screw countersink guide: https://www.eugenefast.com/Home/Page/resources/flat-head-socket-screw-countersink-guide
- Albany County Fasteners: heat-set insert specs (PDF): https://www.albanycountyfasteners.com/media/64/3d/5a/1764619189/heat-set-insert-specs.pdf
- AMES: Helicoil tap sizes (STI): https://amesweb.info/screws/helicoil-tap-sizes.aspx
- MISUMI: Helicoil tap and drill size chart: https://blog.misumiusa.com/helicoil-tap-and-drill-size-chart/