This is an original WWII leather liner strap. The leather is still quite soft and supple, however there are some flaking areas. The curved buckle is green painted steel, dating the strap's production from mid-1943 to mid-1944. It features blackened brass United Carr rivets. This would be an ideal strap for a high-pressure helmet liner with green painted steel A-washers.
WWII Leather Liner Strap With Green Steel Buckle