British Standard Whitworth Thread

The Whitworth thread, introduced by Joseph Whitworth in 1841, was the first national screw thread standard in the world. It featured a 55° thread angle, a depth of 0.640327p, and a radius of 0.137329p, where p represents the pitch.
This thread system later became known as British Standard Whitworth (BSW) and was officially adopted as a British Standard.


Nominal (Inch)
TPI
Pitch (inch)
Thread Depth (inch)
Major Diameter (Inch)
Effective Diameter (inch)
Minor Diameter (inch)
Tap Drill Size(mm)


1/8"
40
0.025
0.016
0.125
0.109
0.0903
2.55 mm

3/16"
24
0.04167
0.0267
0.1875
0.1608
0.1341
3.70 mm

1/4"
20
0.05
0.032
0.25
0.218
0.186
5.10 mm

5/16"
18
0.05556
0.0356
0.3125
0.2769
0.2413
6.50 mm

3/8"
16
0.0625
0.04
0.375
0.335
0.295
7.90 mm

7/16"
14
0.07143
0.0457
0.4375
0.3918
0.3461
9.30 mm

1/2"
12
0.08333
0.0534
0.5
0.4466
0.3932
10.50 mm

9/16"
12
0.08333
0.0534
0.5625
0.5091
0.4557
12.10. mm

5/8"
11
0.09091
0.0582
0.625
0.5668
0.5086
13.50 mm

11/16"
11
0.09091
0.0582
0.6875
0.6293
0.5711
15.00 mm

3/4"
10
0.1
0.064
0.75
0.686
0.622
16.25 mm

7/8"
9
0.11111
0.0711
0.875
0.8039
0.7328
19.25 mm

1"
8
0.125
0.08
1
0.92
0.84
22.00 mm

1-1/8"
7
0.14286
0.0915
1.125
1.0335
0.942
24.75 mm

1-1/4"
7
0.14286
0.0915
1.25
1.1585
1.067
28.00 mm

1-1/2"
6
0.16667
0.1067
1.5
1.3933
1.2866
33.50 mm

1-3/4"
5
0.2
0.1281
1.75
1.6219
1.4938
39.00 mm

2"
4.5
0.22222
0.1423
2
1.8577
1.7154
44.50 mm

TPI, or Threads Per Inch, refers to the number of threads measured along the length of an American fastener. Unlike American fasteners, metric fasteners use thread pitch instead. Generally, smaller fasteners tend to have finer threads, resulting in a higher thread count.