Imperial thread advice needed

[Craizeehair]

I’m not up on the old imperial threads as I’ve only dealt with metric. I’ve just bought an old lathe that I’m currently stripping and trying to get back into a working condition and I have bought some riser blocks to sit it on. The threaded bar supplied isn’t long enough to go through the bench so I need to buy some longer bar which is 5/16” BSF, this bar threads through some adjusting nuts so I can’t just change for something completely different.

When looking, BSW threaded bar is much cheaper than BSF, will this work ok with the BSF nuts, are they compatible with each other?

All I can find online is that one is fine and the other is coarse but does that matter?

[K2-K6]

Both the TPI (threads per inch) and the depth of each pitch (how far it goes inwards from peak) differ from one to the other.

They aren't ordinarily substitute one to the other.

[taysidedragon]

BSF is British Standard Fine.
BSW is British Standard Whitworth, a coarser thread.

They are very different and not interchangeable.

[Craizeehair]

Thank you for that

[Bryanj]

If you are going machining buy a little book called Zeus tables it will explain all the different threads.
If you want to screwcut metric threads on your old imperial lathe you will need a 127 tooth gear wheel