Brass or cycle thread ?

I wasn´t aware that 1/2" 26tpi thread could be BSB (brass) or BSC (cycle) thread when I bought the taps and dies. I see that what I have has BSC or BSCY stamped on them. I want to make fittings for a commercially made Simplex boiler, so I want to know what is normally used for boiler fitting threads. The difference is in the angle, 55 or 60 degree of the thread. I will try finding out from the boiler builder. The drawing does not specify which should be used.

Mike R.

Well if you make your male fittings (assuming all threads on the boiler are female) BSB (55 degree) they will fit either. They are not going to fall out or be significantly weaker for the sake of 2.5 deg on the flank angle!

The only way to be sure what is in the boiler is as you suggest, ask who made it.

Paul.

If you can find or make known threads you can test with engineer's blue which is the best fit.

I would be extremely surprised if Martin Evans had cycle thread in mind when he specified 26tpi threads.

Brass thread was widely specified in ME in the previous century.

duplicate

Edited By Bazyle on 19/11/2018 13:50:24

Gentlemen, please do not mix incompatible threads and in particular where pressure/stress is involved. Yes they will fit together but they WILL be much weaker.

Threads with different angles will screw together providing they have the same pitch but they will bear on the crest and root and not on the flank thus they will not perform as they should. You are compromising safety.

John

Thanks for your replies. The boiler maker confirms it was BSB as expected.

It just shows you have to be careful when buying taps & dies at shows, to look not only at the size and pitch.

I see that this was pointed out by houstonceng in another posting on 10/02/2018.

So I will buy some BSB taps/dies. It is amazing how prices vary between suppliers!