A flanged boiler kit for a 7 1/4 inch gauge engine - although rather enticingly marked "Holmside" on the barrel, that's about the one engine I'm sure it's not.
Barrel:
Length 17 1/2 inch
Diameter 6 3/4 inch
Small tubes 5/8 inch diameter
Superheater flues 1 1/8 inch diameter