I'm not sure there has ever been a concerted effort to date Brilhart pieces based on serial numbers, and unless Brilhart kept records that still exist, no one may ever know for sure. And even if they did, I know the Brilharts made in England do not follow the same pattern as those made in Carlsbad at the same time. So I would guess 50's to mid 60's (Selmer purchased Brilhart in late 60's), but an exact date might be impossible to get.