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UNC (Unified Coarse Thread)

Standardised in 1918

Angle of Thread 60o Degrees

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
inches
T P I Pitch Major Diameter Root Diameter
Internal Threads
Root Diameter
External Threads
Tapping Drill Size
number 1 64 0.0156 0.073 0.0561 0.0538 1.55 mm
(0.610 inch)
number 2 56 0.0179 0.086 0.0667 0.0641 Number Drill 49
(1.85 mm)
number 3 48 0.0208 0.099 0.0764 0.0734 Number Drill 45
(2.1 mm)
number 4 40 0.025 0.112 0.0849 0.0813 2.35 mm
(0.0925 inch)
number 5 40 0.025 0.125 0.0979 0.0943 Number Drill 37
(2.65 mm)
number 6 32 0.0313 0.138 0.1042 0.0997 Number Drill 34
(2.85 mm)
number 8 32 0.0313 0.164 0.1302 0.1257 3.5 mm
(0.1339 inch)
number 10 24 0.0417 0.19 0.1449 0.1389 Number Drill 24
(3.9 mm)
number 12 24 0.0417 0.216 0.1709 0.1649 4.55 mm
(0.1791 inch)
1/4 20 0.05 _ 0.1959 0.1887 Number Drill 7
(5.2 mm)
5/16 18 0.0556 _ 0.2524 0.2443 Letter Drill G
(6.6 mm)
3/8 16 0.0625 _ 0.3073 0.2983 Letter Drill O
(8 mm)
7/16 14 0.0714 _ 0.3602 0.3499 9.4 mm
(0.3701 inch)
1/2 13 0.0769 _ 0.4167 0.4056 10.8 mm
(0.4252 inch)
9/16 12 0.0833 _ 0.4723 0.4603 12.2 mm
(0.4803 inch)
5/8 11 0.0909 _ 0.5266 0.5135 17/32 inch
(13.49 mm)
3/4 10 0.1 _ 0.6417 0.6273 16.5 mm
(0.6496 inch)
7/8 9 0.1111 _ 0.7547 0.7387 49/64 inch
(19.45 mm)
1 inch 8 0.125 _ 0.8647 0.8466 22.25 mm
(0.8760 inch)

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