The stamp of the "7" is the plug gauge. Most gauges were one size larger in number, 1 size smaller in diameter for finishing/polishing, so it looks to be a Birmingham 6 bore but 0.873" is for a 7 bore. Sure they could have been such a thing.

Kind Regards,

Raimey
rse

Last edited by ellenbr; 01/12/09 11:13 PM.