I need to replace the pistons in my 1600HF, having melted one

I thought I had a spare piston, but it turned out to be a 82.6mm, and is too big for the bore.
The pistons in the engine , unfortunately do not have the size stamped on them, only a number cast into the underside which is 092335B I can't identify the make but the symbol on the underside is a circle with a wavey line through it and possibly 3 letters containied within the circle.
Can anyone identify the piston and its bore size, as I currnetly don't have any measuring tools to hand
Cheers
Michael