BSF = British Standard Fine

BSW = British Standard Whitworth.

BSP = British Standard Pipe

BA = British Association

UNF = Unified National Fine

UNC = Unified National Coarse

UNEF = Unified National Extra Fine.

NTP = National Taper Pipe

Whitworth form (and BSF and BSP &nbsp threads are 55 degree while Unified form are 60 degree angle. BA form are 47.5 degree angle. Metric are 60 degree form.

BSW and UNC thread pitches are often the same, as are many BSF and UNF, but DO check! BSP and NTP are different thread form, and the TPI varies as well.

Metric threads are defined by diameter and pitch, so that you can have the standard Metric Coarse, say 12 x 1.75 and a fine version as 12 x1.5 or even finer at 12 x 1.25.

There is no reason why diameter and pitch cannot be non standard. Some Myford lathes used 7/8 x 12 tpi, while then later ones used 1 1/8 x 12 tpi. This is quite common practice for screw fitting chucks for lathes.

Allen Socket Head screws are often referred to as Capscrews. Csk signifies Countersunk head.And then there are Button head and Dome head varieties as well!

HTH

Howard

British Standard Brass is a Whit form thread but with a constant 26 tpi.

Cycle Thread is also 26 tpi, but is 60 degree thread form, so not really interchangeable.

The other variations on the Whitworth thread form are the Model Engineer threads. Most are a constant 40 tpi, while others are 32 tpi.

Howard

Cycle threads, that is BSCy come in a large variety of pitches, not just 26tpi. Motalia have a number of thread charts within their site:

https://www.motalia.co.uk/

Edited By old mart on 25/02/2020 20:03:28

I also would go with Jason,s explanation. I know I am mainly woodworking but I have spent 25+ years in plant repairs dealing with many types of fittings.

I expect it will be like these.

**LINK**

Likely fewer available, rather than buying that many, from other suppliers