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!!!

Reply to
Henry Springer
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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 :-)


Reply to
Jim Guthrie

Is it perhaps because they work out nearer the scale ratio for the model that you are making ?


Reply to
Andrew Mawson

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

Reply to
Dave Croft

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

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Reply to

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'.

Reply to
Tim Christian

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!



Reply to
Mark Howard

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