RB4540 Wayfarer's square front and arms share the same all-acetate build, with 150mm temples — longer than the 140mm metal-frame standard, since acetate Wayfarer styles typically run a bit longer. This aftermarket pair matches that acetate construction and length, so the arm sits and flexes the way it did from the factory rather than the stiffer feel of a metal substitute. The extra 10mm compared to Ray-Ban's metal lines is easy to overlook if you're used to ordering by the more common 140mm figure.

Acetate arms handle differently from metal ones: they don't bend to fit the way metal does, but they resist the hinge play that metal frames eventually develop. The trade-off is that acetate can crack if forced cold, so warming the hinge slightly before adjusting a tight arm avoids snapping it at the pivot. Acetate also holds its color well over time, so a mismatched shade between old and new arms is usually a sign of a different batch rather than fading.