If you have the waist-belt (and not the bandolier), one heavy wire "C" is retained in a folded belt-end and the 'opening' of the C is hooked into the other folded belt-end, to serve as a buckle.
This is the usual use seen in campaign photographs.

In 'training camp' photos, cast U.S. Buckles and Stamped Sheet-Brass Buckles are often seen.

The Cast Buckle was likely retained by using a wire "C" at each belt-end. The cast buckle was snapped onto the wire "C".

The stamped U.S. Plate has fingers on its back that the belt is threaded through.
There is a second, smaller plate, that the other end of the belt is threaded through.
The U.S. Plate neatly hooks on to this smaller plate.

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