This is probably one for kozowy1967 Mark.
I was wondering if this is perhaps another Canadian buckle variation, or something alien to the helmet.
Its on a G.S.W. B.P.& H helmet with 1942 dated V.M.C. liner.
Looks the same as the one posted on Marks pinned thread apart from these slight differences.
It has a rusty blackened steel (not brass) early or post war type buckle on a single type light tan webbing strap. Also the elasticised strap links are steel.
Looking at the pictures on his good pinned thread, they look like the buckles can be removed the way the strap is threaded through the buckle where as mine cannot. I might be wrong.
Unfortunately there are no ink stamps visible.
Anyway I just thought I would let him see it. Because as he says the debate will always go on when these types were made.