UNC — Unified coarse

#12-24 UNC

Tap drill #16 for a #12-24 UNC thread — major Ø 5.486 mm, pitch 1.058 mm (24 TPI).

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Tap drill

#16

4.5 mm · ≈72% thread

Profile

Thread form & key diameters

Dimensions

Designation	#12-24 UNC
Major (outside) diameter	5.486 mm · 0.216"
Pitch	1.058 mm · 24 TPI
Pitch diameter	4.799 mm · 0.1889"
Minor diameter (external)	4.188 mm · 0.1649"
Minor diameter (internal)	4.341 mm · 0.1709"
Recommended tap drill	#16 · 4.5 mm · ≈72% thread
Clearance hole	Close A · Normal D · Loose J — nominal + 1/64" / 1/32" / 1/16" to the nearest standard drill (common shop practice).

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

What tap drill do I need for #12-24 UNC?

For a #12-24 UNC thread, drill the hole with a #16 tap drill (4.5 mm) before tapping. That produces roughly 72% thread engagement, the usual target for a strong, tappable hole. The mating bolt has a major diameter of 5.486 mm and a pitch of 1.058 mm (24 TPI).

To pass a #12-24 UNC bolt through a part rather than thread it, use a clearance hole: Close A · Normal D · Loose J — 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 #12 threads

#12-32 UNEFTap #13Ø 5.486 mm · pitch 0.794 mm #12-28 UNFTap #14Ø 5.486 mm · pitch 0.907 mm

Nearby sizes

More unc — unified coarse threads

#10-24 UNCTap #25Ø 4.826 mm · pitch 1.058 mm 1/4-20 UNCTap #7Ø 6.35 mm · pitch 1.27 mm #8-32 UNCTap #29Ø 4.166 mm · pitch 0.794 mm #6-32 UNCTap #36Ø 3.505 mm · pitch 0.794 mm #5-40 UNCTap #38Ø 3.175 mm · pitch 0.635 mm 5/16-18 UNCTap FØ 7.938 mm · pitch 1.411 mm #4-40 UNCTap #43Ø 2.845 mm · pitch 0.635 mm #3-48 UNCTap #47Ø 2.515 mm · pitch 0.529 mm