Thanks for the links to the linen smoothers information.
I had a look at glass jar lids earlier and they all seem to have a certain diameter on the base to fit into the jar.
what ever this is,it does not seem to have had a hard life. wear on the outer ring of the base but no other marks or blemishes.
That was a reason why i did not think it was an ashtray.
It does not have the look of an old item of glass, but who would be making linen smoothers in the last 50 or 60 years?
The item weighs 1.072 kgs/ 2 lbs 6 ounces.
Tim