These units were also used in shipyards , by welders , electricians & plumbers (& anybody else who picked one up to use) .
I'm guessing late 60's to early 70's .
One sold on ebay last august for $49 or so , but it was slightly older & had a metal handle (a cat#1012) .
Saw 2 others , from $120 to 300 !
Nice & hevi-duty unit there , cap'n !