Martin Evans ‘SIMPLEX’ boiler bush thread form?

[Keith ChartersParticipant @keithcharters25446]

Hi, newbie here. I have a part built ‘SIMPLEX’ with a commercially made boiler. The drawings show that the safety valve, manifold and wet header bushes have threads that are 26tpi (1/2 and 5/8 etc.) but, I cannot find anywhere that states if they are BS Cycle or BS Brass. The thread angle for these two thread forms are different (BSC 60 degrees, BSB 55 degrees). Can anyone  tell me which is used? I need to buy some taps and dies and want to make sure I get the correct ones!

Keith.

[bernard towersParticipant @bernardtowers37738]

I would imagine that its 55deg as BSCY is specifically for cycles/motorcycles, plus I have never seen any fittings (comm or homemade) with BSCY threads.

[Clive Brown 1Participant @clivebrown1]

Yes, absolutely certainly Martin Evans is specifying Brass Thread. This spec. is a useful constant pitch follow on to the common 32tpi ME range which stops at 1/2″. Although frequently described as a “standard” I understand that there is no actual published standard.

1/4″ brass and 1/4″ bsf are the same.

Notwithstanding the above, BSC should be satisfactory, but it’s best to stay with ME tradition.

[Charles LamontParticipant @charleslamont71117]

The ‘Model Engineer’ thread series of 40 & 32 TPI and the 26 TPI ‘Brass’ or ‘Gas’ thread series are all of 55° Whitworth form. Pretty much any UK or Commonwealth design in imperial units will use these threads.

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