YOU MIGHT CHECK WITH ANYONE THAT WORKS IN INDUSTRIAL PLUMBING/BOILERMAKER.
I HAVE MADE BRASS DISCS STAMPED IN THIS SAME MANNER FOR MILLWRIGHTS, MACHINEST
AND INDUSTRIAL PLUMBERS FOR STEAM VALVES AND STEAM CONTROLS TO BE STRAPPED OR CHAINED TO VALVES. THE PROCESS IS THE SAME TODAY AS IT WAS FIFTY YEARS AGO.
I WOULD ASSUME IT WAS THE SAME BACK THEN. A LISCENED BOILERMAKER WOULD MOST
LIKELY HAVE STUDIED THIS.
I HOPE THIS HELPS
PROSPECTORMIKEL
GOOD DAY, GOOD LUCK, AND MAY THE GOOD LORD TAKE A LIKIN' TO YA.