UNF — Unified fine

#4-48 UNF

Tap drill #42 for a #4-48 UNF thread — major Ø 2.845 mm, pitch 0.529 mm (48 TPI).

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Tap drill

#42

2.37 mm · ≈68% thread

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Thread form & key diameters

Dimensions

Designation	#4-48 UNF
Major (outside) diameter	2.845 mm · 0.112"
Pitch	0.529 mm · 48 TPI
Pitch diameter	2.501 mm · 0.0985"
Minor diameter (external)	2.196 mm · 0.0864"
Minor diameter (internal)	2.272 mm · 0.0894"
Recommended tap drill	#42 · 2.37 mm · ≈68% thread
Clearance hole	Close #30 · Normal #27 · Loose #17 — nominal + 1/64" / 1/32" / 1/16" to the nearest standard drill (common shop practice).
Socket key (across flats)	3/32"

Close #30 · Normal #27 · Loose #17 — nominal + 1/64" / 1/32" / 1/16" to the nearest standard drill (common shop practice).

What tap drill do I need for #4-48 UNF?

For a #4-48 UNF thread, drill the hole with a #42 tap drill (2.37 mm) before tapping. That produces roughly 68% thread engagement, the usual target for a strong, tappable hole. The mating bolt has a major diameter of 2.845 mm and a pitch of 0.529 mm (48 TPI).

To pass a #4-48 UNF bolt through a part rather than thread it, use a clearance hole: Close #30 · Normal #27 · Loose #17 — 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 #4 threads

#4-40 UNCTap #43Ø 2.845 mm · pitch 0.635 mm

Nearby sizes

More unf — unified fine threads

#5-44 UNFTap #37Ø 3.175 mm · pitch 0.577 mm #3-56 UNFTap #45Ø 2.515 mm · pitch 0.454 mm #6-40 UNFTap #33Ø 3.505 mm · pitch 0.635 mm #2-64 UNFTap #50Ø 2.184 mm · pitch 0.397 mm #1-72 UNFTap #53Ø 1.854 mm · pitch 0.353 mm #0-80 UNFTap 3/64"Ø 1.524 mm · pitch 0.318 mm #8-36 UNFTap #29Ø 4.166 mm · pitch 0.706 mm #10-32 UNFTap #21Ø 4.826 mm · pitch 0.794 mm