That's a difficult buckle to ID. The width of the larger of the openings in it (about 1.75-inches) suggests it went onto a 1.5-inch wide strap, such as a Suspenders strap. But your buckle's "construction" is so lightweight, I doubt it could withstand the stress of holding up heavy woolen pants. Look how thin the central bar is where the "floating" triple-tongue is crimped onto the central bar. The only such lightweight buckle that comes to mind is a garter-buckle, or perhaps a vest-back adjuster buckle. But those tend to be not that wide.