British Thread Sizes
Here is a list of British Thread Sizes which you may find useful. These lists can be emailed should you require hard copies.
Technical Terms;
TPI - Threads Per Inch, the number of threads per inch length of thread. Place a ruler against a bolt, count the number of peaks, then you have Threads Per Inch.
There are various Thread Forms;
BA - British Association
BSC - British Cycle Thread.
BSF - British Standard Fine.
UNF - Unified Fine Thread.
|
BSC = British Cycle Thread |
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|
SIZE |
THREAD |
TPI |
DIA |
DRILL |
|
1\8 |
BSC |
40 |
0.125 |
0.098 |
|
5\32 |
BSC |
32 |
0.156 |
0.123 |
|
3\16 |
BSC |
32 |
0.188 |
0.154 |
|
7\32 |
BSC |
26 |
0.219 |
0.178 |
|
1\4 |
BSC |
26 |
0.25 |
0.209 |
|
9\32 |
BSC |
26 |
0.281 |
0.24 |
|
5\16 |
BSC |
26 |
0.313 |
0.272 |
|
3\8 |
BSC |
26 |
0.375 |
0.334 |
|
7\16 |
BSC |
26 |
0.438 |
0.397 |
|
1\2 |
BSC |
26 |
0.5 |
0.459 |
|
9\16 |
BSC |
26 |
0.563 |
0.522 |
|
5\8 |
BSC |
26 |
0.625 |
0.584 |
|
11\16 |
BSC |
26 |
0.688 |
0.647 |
|
3\4 |
BSC |
26 |
0.75 |
0.709 |
|
7\16 |
BSC |
20 |
0.438 |
0.384 |
|
1\2 |
BSC |
20 |
0.5 |
0.447 |
|
9\16 |
BSC |
20 |
0.563 |
0.509 |
|
5\8 |
BSC |
20 |
0.625 |
0.572 |
|
11\16 |
BSC |
20 |
0.688 |
0.634 |
|
3\4 |
BSC |
20 |
0.75 |
0.697 |
|
BSF = British Standard Fine |
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|
SIZE |
THEAD |
TPI |
DIA |
DRILL |
|
3\16 |
BSF |
32 |
0.188 |
0.148 |
|
7\32 |
BSF |
28 |
0.219 |
0.173 |
|
1\4 |
BSF |
26 |
0.25 |
0.201 |
|
5\16 |
BSF |
22 |
0.313 |
0.254 |
|
3\8 |
BSF |
20 |
0.375 |
0.311 |
|
7\16 |
BSF |
18 |
0.438 |
0.366 |
|
1\2 |
BSF |
16 |
0.5 |
0.42 |
|
9\16 |
BSF |
16 |
0.563 |
0.483 |
|
5\8 |
BSF |
14 |
0.625 |
0.534 |
|
3\4 |
BSF |
12 |
0.75 |
0.643 |
|
7\8 |
BSF |
11 |
0.875 |
0.759 |
|
SPARK = Spark Plug Thread |
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|
SIZE |
THREAD |
TPI |
DIA |
DRILL |
|
1\4 |
SPARK |
24 |
0.25 |
0.196 |
|
3\8 |
SPARK |
24 |
0.375 |
0.321 |
|
7\8 |
SPARK |
18 |
0.875 |
0.803 |
|
UNF = Unified Fine |
||||
|
SIZE |
THREAD |
TPI |
DIA |
DRILL |
|
1\4 |
UNF |
28 |
0.25 |
0.206 |
|
5\16 |
UNF |
24 |
0.313 |
0.261 |
|
3\8 |
UNF |
24 |
0.375 |
0.324 |
|
7\16 |
UNF |
20 |
0.438 |
0.376 |
|
1\2 |
UNF |
20 |
0.5 |
0.439 |
|
9\16 |
UNF |
18 |
0.563 |
0.494 |
|
5\8 |
UNF |
18 |
0.625 |
0.557 |
|
3\4 |
UNF |
16 |
0.75 |
0.673 |
|
7\8 |
UNF |
14 |
0.875 |
0.787 |