I am doing some research to discover the dimensions of historical sash window bars. I thought perhaps there might be an old joiner about who has repaired original windows and knows. In particular, I wondered if there was a standard size for the glazing rebate.

I have scoured all the old texts, Ellis, Hasluck etc and none of them really seem to say.

The dimensions I’m looking for are A, B and C below.

In general I know A+B+C. It’s given by the size of the moulding plane or template.

I have read that A and B are typically equal. For example, I have a 1 1/2“ sash template, where moulding A can be measured to be 1/2”. If square section B is equal (1/2”) it leaves 1/2” for C - the glazing rebate… perfect. But I doubt that A and B are always equal. And C is unlikely to always be 1/3 the sash depth. But C may always be 1/2”, as glass doesn’t differ much in thickness.

Looking at the Mathieson catalogue from 1900ish, they have sash planes for many sizes of bars available:

Here they show a 2 1/4” glazing bar, probably for a shop front. I can’t believe that the glazing rebate is 2/3“! There must be a standard, which may have been lost in the mists of time.

If anyone knows the answer or where to find out, that would be really helpful. (Hint - the answer is not in mm!)

Steve