ME nuts and bolts

Edited By Ian S C on 13/02/2012 00:59:35

Peter The origins of M.E. threads are a bit of a mystery. There are TWO variants available today these are the 40 TPI and the 32 TPI. Both are in the Whitworth thread form.

They were designed for simplicity of manufacture and for use in thin materials. Most model engineer’s lathes of the pre-war period had 8TPI lead screws. With a 40 or a 32 TPI threads you can ‘drop in’ anywhere. There may have been a coarser thread of 24 TPI but it may have been lost. For ME size bolts from ¼” up I use BSF (as I have the taps and dies). Foe smaller than ¼” (6mm downwards I tend to use the now illegal BAs.

The third set of threads, called ME are the 26 TPI threads. These are the ‘Brass’ or ‘Birmingham Brass’ threads. These are used on most boiler fittings. The 26TPI ‘Birmingham Brass’, which are again in the Whitworth thread form, should not be confused with the old 26TPI Standard Bicycle threads which have a different thread form. I will not go into them here, except to say that taps and dies of this series are marked with a letter ‘C’.

Finally The BA series threads which were introduced at the turn of the last centenary. Here the sizes run from the largest ‘0’ BA down to ‘24’ BA. They are said by the authorities to be inch standard and therefore forbidden in The EU. BA threads are not inch standard. The starting size ‘0’Ba is 6mm with a 1mm pitch with a 47.5° angle. The smaller sizes have a pitch which is 90% of the size larger so, 1BA has a pitch of 0.9mm, 2BA 0.89mm and so on down to 25 BA which has bar diameter of 0.25mm. If you want more look here.

Do not let your local authority know you have BA sizes they will do their nuts according to them (even now) all Non metric threads are illegal!! You try to tell them that and unless you have several £1000 to throw away they will throw the book at you.