Dean Nickel wrotePending patent…. that would put it to the beginning years.
Master actually kept the “Patent Pending” mark on these for much of the 1940s. Same with the #47 and #48 padlocks, which didn’t have the markings updated until not long before they were discontinued in 1948.
I’d say this lock is probably from the 1940s considering the tiny details like the typeface of the serial number marking on the back. Possibly the late ’30s but probably some time in the ’40s. Check out the thread Pete linked to for photos of one just like this but with a steel case (apparently made circa the time of WWII; perhaps it was done to conserve brass for war use) as well as photos of the short-lived #100 model, which had a nickel-silver case and, until late in its production, 4 cams, therefore having many more combinations.
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