Thread types

[Groily]

Thanks Bill. Thinking about it (for the first time in 60 fettling years), I'm pretty sure I use a Whit spanner on my single's rocker cover bolts which have a 5/16" BSF thread form.

That you would Neville! The spanner might be marked 1/4W and 5/16BSF.
For a given size whitform fastener, nuts and bolt heads are 'one size up' in W (or 'one down' in BSF or BSC) - it runs according to shank diameters not the AF measurement. BSW needs chunkier nuts 'cos the coarse thread cuts deep.
There do seem to be cheapo spanners out there with just the one marking these days though.

[Andy51]

The only Whitworth thread on my '54 18S is the 1/4 thread for the handlebar clamp. All the rest are BSF and BSC with the exception of the BSP for oil and petrol fittings and a few small BA screws. BSF, BSW and BSC all have the same head dimensions and use the same spanners, as do some but not all BSP. A set of BSC taps/ dies + 1/4 BSW, 5/16 and 3/8 BSF should cover normal use, get BSP and 2BA if required. As has been said Tracy tools have virtually everything.

[ChrisTheChippy]

Or go chepo if you are a skinflint like me and pick a lot of spanners taps dies etc from car boot sales. If you are prepared to rummage its amazing what you find.

[Steve64]

Gee wizz guys, what a wealth of knowledge, thanks for all of that info, it helps a great deal. Much appreciated .
Steve.