UNF — Unified fine

#10-32 UNF

Tap drill #21 for a #10-32 UNF thread — major Ø 4.826 mm, pitch 0.794 mm (32 TPI).

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Tap drill

#21

4.04 mm · ≈76% thread

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Thread form & key diameters

Dimensions

Designation	#10-32 UNF
Major (outside) diameter	4.826 mm · 0.19"
Pitch	0.794 mm · 32 TPI
Pitch diameter	4.31 mm · 0.1697"
Minor diameter (external)	3.852 mm · 0.1517"
Minor diameter (internal)	3.967 mm · 0.1562"
Recommended tap drill	#21 · 4.04 mm · ≈76% thread
Clearance hole	Close #5 · Normal #2 · Loose 1/4" — nominal + 1/64" / 1/32" / 1/16" to the nearest standard drill (common shop practice).
Socket key (across flats)	5/32"

Close #5 · Normal #2 · Loose 1/4" — nominal + 1/64" / 1/32" / 1/16" to the nearest standard drill (common shop practice).

What tap drill do I need for #10-32 UNF?

For a #10-32 UNF thread, drill the hole with a #21 tap drill (4.04 mm) before tapping. That produces roughly 76% thread engagement, the usual target for a strong, tappable hole. The mating bolt has a major diameter of 4.826 mm and a pitch of 0.794 mm (32 TPI).

To pass a #10-32 UNF bolt through a part rather than thread it, use a clearance hole: Close #5 · Normal #2 · Loose 1/4" — 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 #10 threads

#10-24 UNCTap #25Ø 4.826 mm · pitch 1.058 mm

Nearby sizes

More unf — unified fine threads

#8-36 UNFTap #29Ø 4.166 mm · pitch 0.706 mm #12-28 UNFTap #14Ø 5.486 mm · pitch 0.907 mm #6-40 UNFTap #33Ø 3.505 mm · pitch 0.635 mm 1/4-28 UNFTap #3Ø 6.35 mm · pitch 0.907 mm #5-44 UNFTap #37Ø 3.175 mm · pitch 0.577 mm #4-48 UNFTap #42Ø 2.845 mm · pitch 0.529 mm #3-56 UNFTap #45Ø 2.515 mm · pitch 0.454 mm #2-64 UNFTap #50Ø 2.184 mm · pitch 0.397 mm