Unified Thread Standard (UNC/UNF) Conversion Table

The pitch of a screw is defined by the angle of its threads - a coarse pitch will have a more obtuse thread angle, whereas a fine pitch will have a shallower thread angle, resulting in a greater number of threads on the screw itself, and a more secure fastening.

The Unified Thread Standard is an imperial thread standard used across the majority of Accu's imperial fastener ranges. Components using UTS threads generally fall into two categories, UNC (Unified Coarse) and UNF (Unified Fine).  UNEF (Unified Extra Fine) can also be made available on components which are manufactured to order. For the tooling used to identifying unknown thread types, please see Accu's ranges of UNS Thread Gauges.

Sizes within the Unified Thread Standard are designated using two numbers – the first represents the major diameter of the thread, and the second represents the pitch of the screw thread in threads per inch (TPI).

For instance, a UTS thread of 1/4-20 will have a diameter of 1/4 inch, and 20 threads per inch.

For thread sizes smaller than 1/4 inch, a numerical size such as No.1 (Or #1) is used.

For more general information on the conversion between metric and imperial measurements, please see our Metric to Imperial Conversion Table.

Major Diameter (inch/mm)Thread Density (d) and Thread Pitch (p)
Coarse Pitch (UNC)Fine Pitch (UNF)Extra Fine Pitch (UNEF)
d (TPI)p (inch/mm)d (TPI)p (inch/mm)d (TPI)p (inch/mm)
No. 00.0600 / 1.5240N/A800.12500 / 0.3175N/A
No. 10.0730 / 1.8542640.015625 / 0.3969720.013888 / 0.3528N/A
No. 20.0860 / 2.1844560.017857 / 0.4536640.015625 / 0.3969N/A
No. 30.0990 / 2.5146480.020833 / 0.5292560.017857 / 0.4536N/A
No. 40.1120 / 2.8448400.025000 / 0.6350480.020833 / 0.5292N/A
No. 50.1250 / 3.1750400.025000 / 0.6350440.022727 / 0.5773N/A
No. 60.1380 / 3.5052320.031250 / 0.7938400.025000 / 0.6350N/A
No. 80.1640 / 4.1656320.031250 / 0.7938360.027778 / 0.7056N/A
No. 100.1900 / 4.8260240.041667 / 1.0583320.031250 / 0.7938N/A
No. 120.2160 / 5.4864240.041667 / 1.0583280.035714 / 0.9071320.031250 / 0.7938
1/40.2500 / 6.3500200.050000 / 1.2700280.035714 / 0.9071320.031250 / 0.7938
5/160.3125 / 7.9375180.055556 / 1.4111240.041667 / 1.0583320.031250 / 0.7938
3/80.3750 / 9.5250160.062500 / 1.5875240.041667 / 1.0583320.031250 / 0.7938
7/160.4375 / 11.1125140.071428 / 1.8143200.050000 / 1.2700280.035714 / 0.9071
1/20.5000 / 12.7000130.076923 / 1.9538200.050000 / 1.2700280.035714 / 0.9071
9/160.5625 / 14.2875120.083333 / 2.1167180.055556 / 1.4111240.041667 / 1.0583
5/80.6250 / 15.8750110.090909 / 2.3091180.055556 / 1.4111240.041667 / 1.0583
3/40.7500 / 19.0500100.100000 / 2.5400160.062500 / 1.5875200.050000 / 1.2700
7/80.8750 / 22.225090.111111 / 2.8222140.071428 / 1.8143200.050000 / 1.2700
11.0000 / 25.400080.125000 / 3.175012/140.083333 / 2.1167200.050000 / 1.2700

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