All about threads

WHIT: Whitworth Form
BSW:British Standard Whitworth
Tap Size Threads perInch Tap Form Drill size mm
1/16 60 WHIT 1.2
3/32 48 WHIT 1.9
1/8 40 BSW 2.55
5/32 32 WHIT 3.2
3/16 24 BSW 3.7
7/32 24 WHIT 4.5
1/4 20 BSW 5.1
5/16 18 OSW 6.5
3/8 16 BSW 7.9
7/16 14 BSW 9.5
1/2 12 BSW 10.5
9/16 12 BSW 12.2
5/8 11 BSW 13.5
3/4 10 BSW 16.5
7/8 9 BSW 19.5
1 8 BSW 22.0
1-1/8 7 BSW 25.0
1-1/4 7 BSW 28.0
1-1/2 6 BSW 33.5
1-3/4 5 BSW 39.0
2 4-1/2 BSW 44.5
BSF:British Standard Fine
Tap Size Threadsperinch Drill size mm
3/16 32 4.0
1/4 26 5.3
5/16 22 6.8
3/8 20 8.3
7/16 18 9.8
1/2 16 11.2
9/16 16 12.8
5/8 14 14.0
3/4 12 17.0
7/8 11 20.0
1 10 23.0
1 1/4 9 28.5
1 1/2 8 34.5
1 3/4 7 40.5

Metric ISO Coarse Metric Selected Fine
Tap Size Pitch mm Drill size mm Tap Size Pitch mm Drill size mm
2.0 .40 1.65 8.0 1.00 7.1
2.5 .45 2.1 10.0 1.25 8.9
3.0 .50 2.55 12.0 1.50 10.5
3.5 .60 2.95 14.0 1.50 12.5
4.0 .70 3.4 16.0 1.50 14.5
4.5 .75 3.8 18.0 1.50 16.5
5.0 .80 4.3 20.0 1.50 18.5
6.0 1.00 5.1 22.0 1.50 20.5
7.0 1.00 6.1 24.0 2.00 22.0
8.0 1.25 6.9
9.0 1.25 7.9
10.0 1.50 8.6
11.0 1.50 9.5
12.0 1.75 10.2
14.0 2.00 12.2
16.0 2.00 14.25
18.0 2.50 15.75
20.0 2.50 17.5
22.0 2.50 19.5
24.0 3.00 21.0
27.0 3.00 24.0
30.0 3.50 26.5
33.0 3.50 29.5
36.0 4.00 32,0

ANPT: American National Pipe Straight ANPS: American National PipeStraight (Parallel)
Tap Size Pipe Taper mm Tap size Threads per inch Drill size mm
1/8 27 8.4 1/8 27 8.7
1/4 18 11.2 1/4 18 11.2
3/8 18 14.25 3/8 18 15.0
1/2 14 17.5
3/4 14 23.0
1 11.5 29.0
1.25 11.5 37.5
1.5 11.5 44.0
2 11.5 56.0

Spark Plug
Tap size Pitch mm Drill size mm
10.0 1.0 9.0
12.0 1.25 10.5
14.0 1.25 12.5
18.9 1.5 16.5

UNC: Unified National Coarse UNF: Unified National Fine UNS: Unified National Special
Tap Size Threads perinch Drill Size mm Tap size Threads per inch Drill size mm Tap size Threads per inch Drill size mm
2 56 1.85 2 64 1.90 1/8 40 2.65
3 48 2.10 3 56 2.15 5/32 32 3.3
4 40 2.35 4 48 2.40 3/16 24 3.8
5 40 2.65 5 44 2.7 32 4.1
6 32 2.85 6 40 2.95 7/32 24 4.6
8 32 3.5 8 36 3.5 32 4.9
10 24 3.9 10 32 4.1 11/16 11 15.25
12 24 4.5 12 28 4.7 11/16 16 16.0
1/4 20 5.1 1/4 28 5.5 13/16 10 18.5
5/16 18 6.6 5/16 24 6.9 13/16 16 19.0
3/8 16 8.0 3/8 24 8.5 1 14 23.5
7/16 14 9.5 7/16 20 10.0
1/2 13 10.8 1/2 20 11.5
9/16 12 12.2 9/16 18 12.8
5/8 11 13.5 5/8 18 14.5
3/4 10 16.5 3/4 16 17.5
7/8 9 19.5 7/8 14 20.5
1 8 22.5 1 12 23.5
1-1/8 7 25,0 1-1/8 12 26,5
1-1/4 7 28.0 1-1/4 12 29.5
1-3/8 6 31.0 1-3/8 12 33.0
1-1/2 6 34.0 1-1/2 12 36.0

British Standard Pipe Taper ISO Series ‘RC’ British Standard Pipe Parallel ISO Series ‘G’
Tap Size TPI Reamer Drill Size Tap Size TPI Drill Size
1/8 28 18.0 1/8 28 8.8
1/4 19 10.8 1/4 19 11.8
3/8 19 14.25 3/8 19 15.25
1/2 14 17.5 1/2 14 19.0
3/4 14 23.0 5/8 14 21.0
1 11 29.0 3/4 14 24.5
1 1/4 11 37.5 7/8 14 28.5
1 1/2 11 43.5 1 11 30.5
2 11 55.0 1-1/4 11 39.5
1-1/2 11 45.5
2 11 57.0
2-1/2 11 72.5