Maybe it didn't matter that much at the time when they refurbished them, but a year later in 1938 they had the stainless steel rim.
The Australians & Newzealanders had a raw edge in WW2, plus the BMB 1941 was raw edge, & then there is the BMB made 1953 Mk4 that was rimless.
Here's a couple of pics of the Mk1 & Mk2 chin strap lugs, both on a Mk1*.
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