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Unified Pitch Diameter Combinations

Sizesa No. or Inches Basic Major Dia. Inches Threads per Inch
Series with Graded Pitches Series with Uniform (Constant) Pitches
Coarse UNC Fineb UNF Extra finec UNEF 4-UN 6-UN 8-UN 12-UN 16-UN 20-UN 28-UN 32-UN
0 0.06" ... 80 Series designation shown indicates the UN thread form; however, the UNR thread form may be specified by substituting UNR in place of UN in all designations for external threads.
1 0.073" 64 72
2 0.086" 56 64
3 0.099" 48 56
4 0.112" 40 48
5 0.125" 40 44 ... ... ... ... ... ... ... ... ...
6 0.138" 32 40 ... ... ... ... ... ... ... ... UNC
8 0.164" 32 36 ... ... ... ... ... ... ... ... UNC
10 0.19" 24 32 ... ... ... ... ... ... ... ... UNF
12 0.216" 24 28 32 ... ... ... ... ... ... UNF UNEF
1⁄4 0.25" 20 28 32 ... ... ... ... ... UNC UNF UNEF
5⁄16 0.3125" 18 24 32 ... ... ... ... ... 20 28 UNEF
3⁄8 0.375" 16 24 32 ... ... ... ... UNC 20 28 UNEF
7⁄16 0.4375" 14 20 28 ... ... ... ... 16 UNF UNEF 32
1⁄2 0.5" 13 20 28 ... ... ... ... 16 UNF UNEF 32
9⁄16 0.5625" 12 18 24 ... ... ... UNC 16 20 28 32
5⁄8 0.625" 11 18 24 ... ... ... 12 16 20 28 32
(11⁄16) 0.6875" ... ... 24 ... ... ... 12 16 20 28 32
3⁄4 0.75" 10 16 20 ... ... ... 12 UNF UNEF 28 32
(13⁄16) 0.8125" ... ... 20 ... ... ... 12 16 UNEF 28 32
7⁄8 0.875" 9 14 20 ... ... ... 12 16 UNEF 28 32
(15⁄16) 0.9375" ... ... 20 ... ... ... 12 16 UNEF 28 32
1 1" 8 12 20 ... ... UNC UNF 16 UNEF 28 32
(1 1⁄16) 1.0625" ... ... 18 ... ... 8 12 16 20 28 ...
1 1⁄8 1.125" 7 12 18 ... ... 8 UNF 16 20 28 ...
(1 3⁄16) 1.1875" ... ... 18 ... ... 8 12 16 20 28 ...
1 1⁄4 1.25" 7 12 18 ... ... 8 UNF 16 20 28 ...
1 5⁄16 1.3125" ... ... 18 ... ... 8 12 16 20 28 ...
1 3⁄8 1.375" 6 12 18 ... UNC 8 UNF 16 20 28 ...
(1 7⁄16) 1.4375" ... ... 18 ... 6 8 12 16 20 28 ...
1 1⁄2 1.5" 6 12 18 ... UNC 8 UNF 16 20 28 ...
(1 9⁄16) 1.5625" ... ... 18 ... 6 8 12 16 20 ... ...
1 5⁄8 1.625" ... ... 18 ... 6 8 12 16 20 ... ...
(1 11⁄16) 1.6875" ... ... 18 ... 6 8 12 16 20 ... ...
1 3⁄4 1.75" 5 ... ... ... 6 8 12 16 20 ... ...
(1 13⁄16) 1.8125" ... ... ... ... 6 8 12 16 20 ... ...
1 7⁄8 1.875" ... ... ... ... 6 8 12 16 20 ... ...
(1 15⁄16) 1.9375" ... ... ... ... 6 8 12 16 20 ... ...
2 2" 41⁄2 ... ... ... 6 8 12 16 20 ... ...
(2 1⁄8) 2.125" ... ... ... ... 6 8 12 16 20 ... ...
2 1⁄4 2.25" 4 1⁄2 ... ... ... 6 8 12 16 20 ... ...
(2 3⁄8) 2.375" ... ... ... ... 6 8 12 16 20 ... ...
2 1⁄2 2.5" 4 ... ... UNC 6 8 12 16 20 ... ...
(2 5⁄8) 2.625" ... ... ... 4 6 8 12 16 20 ... ...
2 3⁄4 2.75" 4 ... ... UNC 6 8 12 16 20 ... ...
(2 7⁄8) 2.875" ... ... ... 4 6 8 12 16 20 ... ...
3 3" 4 ... ... UNC 6 8 12 16 20 ... ...
(3 1⁄8) 3.125" ... ... ... 4 6 8 12 16 ... ... ...
3 1⁄4 3.25" 4 ... ... UNC 6 8 12 16 ... ... ...
(3 3⁄8) 3.375" ... ... ... 4 6 8 12 16 ... ... ...
3 1⁄2 3.5" 4 ... ... UNC 6 8 12 16 ... ... ...
(3 5⁄8) 3.625" ... ... ... 4 6 8 12 16 ... ... ...
3 3⁄4 3.75" 4 ... ... UNC 6 8 12 16 ... ... ...
(3 7⁄8) 3.875" ... ... ... 4 6 8 12 16 ... ... ...
4 4" 4 ... ... UNC 6 8 12 16 ... ... ...
  • a) Sizes shown in parentheses are secondary sizes. Primary sizes of 41 ⁄ 4, 41 ⁄ 2, 43 ⁄ 4, 5, 51 ⁄ 4, 51 ⁄ 2, 53 ⁄ 4 and 6 inches also are in the 4, 6, 8, 12, and 16 thread series; secondary sizes of 41 ⁄ 8, 43 ⁄ 8, 45 ⁄ 8, 47 ⁄ 8, 51 ⁄ 8, 53 ⁄ 8, 55 ⁄ 8, and 57 ⁄ 8 also are in the 4, 6, 8, 12, and 16 thread series. Basic Major Dia. Inches Threads per Inch Series with Graded Pitches Series with Uniform (Constant) Pitches Coarse UNC Fineb UNF
  • b) For diameters over 11 ⁄ 2 inches, use 12-thread series. Extra finec UNEF
  • c) For diameters over 111⁄ 16 inches, use 16-thread series.
  • For UNR thread form substitute UNR for UN for external threads only.