This is a solid cast brass Deep D ring which has been plated in nickel for a silver coloured finish.
It measures 1"(25mm) across the inside of the straight edge.
Cast D rings are much stronger than wire formed, and recommended for use on dog collars horse tack etc. They're also great for attaching straps to handbags etc.
These rounded heavy dees have an internal depth of approximately 22mm from the straight bar to the centre of the curve.