York "A" Plates

I have been scouring the internet and cannot find much information about York A plates.  They seem desirable, they are hard to identify and now I want some.  It appears to be a standard plate with a unique rim and marked as 10A, 5A, 2.5A, etc.

Per Ben Beaulieu

They are Yorks first gen 1 inch plates. Same design that was stolen from Jowetts plates. Jowett plates also have the A stamps.

I believe York A plates from from the early 1930’s - mid 1930’s. Then Yorks switched to the wide letter single side plates from mid to late 1930’s. The started casting the wide letter double sided.

The A plates are a very cool set. I like collecting these mainly for the fact of the age and I like anything pre-war or WW2 era.