UNF — Unified fine

#12-28 UNF

Tap drill #14 for a #12-28 UNF thread — major Ø 5.486 mm, pitch 0.907 mm (28 TPI).

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Tap drill

#14

4.62 mm · ≈73% thread

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Thread form & key diameters

Dimensions

Designation	#12-28 UNF
Major (outside) diameter	5.486 mm · 0.216"
Pitch	0.907 mm · 28 TPI
Pitch diameter	4.897 mm · 0.1928"
Minor diameter (external)	4.373 mm · 0.1722"
Minor diameter (internal)	4.504 mm · 0.1773"
Recommended tap drill	#14 · 4.62 mm · ≈73% 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 #12-28 UNF?

For a #12-28 UNF thread, drill the hole with a #14 tap drill (4.62 mm) before tapping. That produces roughly 73% 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 0.907 mm (28 TPI).

To pass a #12-28 UNF 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 #12-24 UNCTap #16Ø 5.486 mm · pitch 1.058 mm

Nearby sizes

More unf — unified fine threads

#10-32 UNFTap #21Ø 4.826 mm · pitch 0.794 mm 1/4-28 UNFTap #3Ø 6.35 mm · pitch 0.907 mm #8-36 UNFTap #29Ø 4.166 mm · pitch 0.706 mm #6-40 UNFTap #33Ø 3.505 mm · pitch 0.635 mm #5-44 UNFTap #37Ø 3.175 mm · pitch 0.577 mm 5/16-24 UNFTap IØ 7.938 mm · pitch 1.058 mm #4-48 UNFTap #42Ø 2.845 mm · pitch 0.529 mm #3-56 UNFTap #45Ø 2.515 mm · pitch 0.454 mm