UNC — Unified coarse

#3-48 UNC

Tap drill #47 for a #3-48 UNC thread — major Ø 2.515 mm, pitch 0.529 mm (48 TPI).

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Tap drill

#47

1.99 mm · ≈76% thread

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Thread form & key diameters

Dimensions

Designation	#3-48 UNC
Major (outside) diameter	2.515 mm · 0.099"
Pitch	0.529 mm · 48 TPI
Pitch diameter	2.171 mm · 0.0855"
Minor diameter (external)	1.865 mm · 0.0734"
Minor diameter (internal)	1.942 mm · 0.0764"
Recommended tap drill	#47 · 1.99 mm · ≈76% thread
Clearance hole	Close #32 · Normal #30 · Loose #20 — nominal + 1/64" / 1/32" / 1/16" to the nearest standard drill (common shop practice).
Socket key (across flats)	5/64"

Close #32 · Normal #30 · Loose #20 — nominal + 1/64" / 1/32" / 1/16" to the nearest standard drill (common shop practice).

What tap drill do I need for #3-48 UNC?

For a #3-48 UNC thread, drill the hole with a #47 tap drill (1.99 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 2.515 mm and a pitch of 0.529 mm (48 TPI).

To pass a #3-48 UNC bolt through a part rather than thread it, use a clearance hole: Close #32 · Normal #30 · Loose #20 — 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 #3 threads

#3-56 UNFTap #45Ø 2.515 mm · pitch 0.454 mm

Nearby sizes

More unc — unified coarse threads

#4-40 UNCTap #43Ø 2.845 mm · pitch 0.635 mm #2-56 UNCTap #50Ø 2.184 mm · pitch 0.454 mm #5-40 UNCTap #38Ø 3.175 mm · pitch 0.635 mm #1-64 UNCTap #53Ø 1.854 mm · pitch 0.397 mm #6-32 UNCTap #36Ø 3.505 mm · pitch 0.794 mm #8-32 UNCTap #29Ø 4.166 mm · pitch 0.794 mm #10-24 UNCTap #25Ø 4.826 mm · pitch 1.058 mm #12-24 UNCTap #16Ø 5.486 mm · pitch 1.058 mm