RB3557 doesn't carry a shape nickname the way some Ray-Ban models do, but its spec is specific enough: a 145mm metal arm on a square front, which is what this aftermarket pair is cut to. At 145mm it sits between the 140mm arms used on several other square-metal Ray-Bans and the 150mm used on some acetate Wayfarer models, so it's not a length to guess at.

A square metal arm this length wears in the usual places — the hinge screw loosening first, then eventually the tip sleeve near the ear hardening or splitting. Neither issue affects the front frame, which is why a replacement arm, rather than a whole new pair of sunglasses, is the proportionate fix when only the temple has given out. Confirming the 145mm figure against the arm you're replacing takes a minute and rules out the two closest-looking alternatives in the range.