BA

Henry,

I think it is because 5 and 7BA are close to the Imperial 1/8" and

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