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British Threads - UNC


UNC (Unified Coarse Thread)

Standardised in 1918

Angle of Thread 60°

UNC Thread Profile

American threads consist of two common thread patterns known as U.N.F and U.N.C.

U.N.F [national fine] is exactly the same as the old S.A.E [standard american engineers] that existed before threads were unified.

U.N.C [national coarse] roughly derived from the British Whitworth having the same pitches except 1/2 in dia where Whitworth is 12tpi and U.N.C is 13 tpi.

Both these threads are 60 degree angle.

Early Harley and Indian motorcycles used 24tpi threads on most diameters 5/16 and 3/8 UNF are both 24tpi.

7/32 x 24 UNC is an obsolete thread


diameter in
T P IPitchMajor DiameterRoot Diameter
Internal Threads
Root Diameter
External Threads
Tapping Drill Size
number 1640.01560.0730.05610.05381.55 mm
(0.610 inch)
number 2560.01790.0860.06670.0641Number Drill 49
(1.85 mm)
number 3480.02080.0990.07640.0734Number Drill 45
(2.1 mm)
number 4400.0250.1120.08490.08132.35 mm
(0.0925 inch)
number 5400.0250.1250.09790.0943Number Drill 37
(2.65 mm)
number 6320.03130.1380.10420.0997Number Drill 34
(2.85 mm)
number 8320.03130.1640.13020.12573.5 mm
(0.1339 inch)
number 10240.04170.190.14490.1389Number Drill 24
(3.9 mm)
number 12240.04170.2160.17090.16494.55 mm
(0.1791 inch)
1/4200.05_0.19590.1887Number Drill 7
(5.2 mm)
5/16180.0556_0.25240.2443Letter Drill G
(6.6 mm)
3/8160.0625_0.30730.2983Letter Drill O
(8 mm)
7/16140.0714_0.36020.34999.4 mm
(0.3701 inch)
1/2130.0769_0.41670.405610.8 mm
(0.4252 inch)
9/16120.0833_0.47230.460312.2 mm
(0.4803 inch)
5/8110.0909_0.52660.513517/32 inch
(13.49 mm)
3/4100.1_0.64170.627316.5 mm
(0.6496 inch)
7/890.1111_0.75470.738749/64 inch
(19.45 mm)
1 inch80.125_0.86470.846622.25 mm
(0.8760 inch)