UNC — Unified coarse

#8-32 UNC

Tap drill #29 for a #8-32 UNC thread — major Ø 4.166 mm, pitch 0.794 mm (32 TPI).

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Tap drill

#29

3.45 mm · ≈69% thread

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Thread form & key diameters

Dimensions

Designation	#8-32 UNC
Major (outside) diameter	4.166 mm · 0.164"
Pitch	0.794 mm · 32 TPI
Pitch diameter	3.65 mm · 0.1437"
Minor diameter (external)	3.192 mm · 0.1257"
Minor diameter (internal)	3.306 mm · 0.1302"
Recommended tap drill	#29 · 3.45 mm · ≈69% thread
Clearance hole	Close #15 · Normal #9 · Loose #1 — nominal + 1/64" / 1/32" / 1/16" to the nearest standard drill (common shop practice).
Socket key (across flats)	9/64"

Close #15 · Normal #9 · Loose #1 — nominal + 1/64" / 1/32" / 1/16" to the nearest standard drill (common shop practice).

What tap drill do I need for #8-32 UNC?

For a #8-32 UNC thread, drill the hole with a #29 tap drill (3.45 mm) before tapping. That produces roughly 69% thread engagement, the usual target for a strong, tappable hole. The mating bolt has a major diameter of 4.166 mm and a pitch of 0.794 mm (32 TPI).

To pass a #8-32 UNC bolt through a part rather than thread it, use a clearance hole: Close #15 · Normal #9 · Loose #1 — nominal + 1/64" / 1/32" / 1/16" to the nearest standard drill (common shop practice)..

All values are generated from the standard thread formulas (ISO 68-1 / ASME B1.1) and published standard tables — not hand-entered. See the full reference.

Same diameter

Other #8 threads

#8-36 UNFTap #29Ø 4.166 mm · pitch 0.706 mm

Nearby sizes

More unc — unified coarse threads

#10-24 UNCTap #25Ø 4.826 mm · pitch 1.058 mm #6-32 UNCTap #36Ø 3.505 mm · pitch 0.794 mm #5-40 UNCTap #38Ø 3.175 mm · pitch 0.635 mm #12-24 UNCTap #16Ø 5.486 mm · pitch 1.058 mm #4-40 UNCTap #43Ø 2.845 mm · pitch 0.635 mm #3-48 UNCTap #47Ø 2.515 mm · pitch 0.529 mm #2-56 UNCTap #50Ø 2.184 mm · pitch 0.454 mm 1/4-20 UNCTap #7Ø 6.35 mm · pitch 1.27 mm