I'm an electrical engineer. We use (or used) even BA szes for terminals. I have many sets of enven number BA spanners, sockets, nut runners etc. I'm now building a steam engine and everthing is ODD BA sizes. Why!!!
Henry,
I think it is because 5 and 7BA are close to the Imperial 1/8" and
3/32" diameters.Like you, I've had to buy 5 and 7BA sets for Stuart Turner models :-)
Jim.
Is it perhaps because they work out nearer the scale ratio for the model that you are making ?
AWEM
As an Ex-BT Electro-Mechanical telephone engineer ISTR being told that the odd BA sizes tended to be used for mechanical use & Even BA for Electrical terminals.
-- Dave Croft Warrington
stuart turner use the odd sizes as the heads look more to scale, howeve
you can also get even BA sizes with smaller sized head
-- bolma
----------------------------------------------------------------------- bolmas's Profile:
Electronics (in the '60s) used even BA sizes, electrics (mains plugs and sockets, for example) used odd BA.
To bridge the gap, Radiospares (now RS Components) supplied a small box with the interesting title 'Odd Screw Kit'.
Two of the possible reasons are:
Electrical equipment tends to use even no's, whereas mechanical sometimes seem to use odd no's.
Scale models often use 'one size smaller' nuts and screw heads - so a 5BA thread has a 6BA head/nut diameter etc.
Other than those possibles, I haven't a clue!
Regards
Mark
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