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Identifying The Size Of A Thread

By Admin on Fri 10 February 2017 in Solenoid Valve FAQ's

There are many different thread standards used in the engineering industry but by far the most common in the UK and any former commonwealth Countries is BSP (British Standard Pipe). In this post we will help you to identify what thread size you have.

A common mistake is to simply measure the inside diameter of the pipe and assume that this measurement will be the thread size you are after. For example if you measure 25mm you may think that is is a 1” BSP but in fact it is ¾” BSP as this measurement fits between the major and minor diameter for this size. You really need to think of the thread size required as the “Trade Size” as this is what the thread size is known as in the industry (not as a direct correlation to the size you measure). To help you establish what size thread you have you measure the id of your pipe to find where that measurement falls between the major and minor diameter. This is then your size (All dimensions in mm).

 

Trade Size (BSP) Pitch Major Diameter Minor Diameter Gage Length
1/8 0.907 9.728 8.565 3.97
1/4 1.337 13.157 11.445 6.012
3/8 1.337 16.662 14.95 6.35
1/2 1.814 20.955 18.633 8.164
3/4 1.814 26.441 24.12 9.525
1 2.309 33.249 30.292 10.391
1 ¼ 2.309 41.91 38.953 12.7
1 ½ 2.309 47.803 44.846 12.7
2 2.309 59.614 56.657 15.875
2 ½ 2.309 75.184 72.227 17.463
3 2.309 87.884 84.927 20.638
4 2.309 113.03 110.073