The RB1969 Rectangle is the sunglasses version of Ray-Ban's 1969 frame, built with a rectangular metal front and 140mm metal arms. This aftermarket set matches that straight-edged profile, so the arm sits flush against the front the same way it does on the factory pair, rather than curving in like an oval or round style would. The RX1969V prescription version shares the same rectangular shape, so the RB prefix is what marks this as the sunglasses variant specifically.

Rectangular metal sunglasses like this one are usually stored folded in a case more than worn on a cord, which puts repeated stress on the hinge fold rather than on the lenses or front. If the arms have gotten loose or won't stay folded flat, that's ordinary hinge wear, not a sign the frame is failing. A stiff new hinge that loosens slightly over the first few weeks of wear is normal and not a sign the arm was cut wrong.