This aftermarket pair is cut to the Ray-Ban RB3857 Frank spec: 145mm metal arms shaped for a rectangular hinge mount, matching what the frame is built around. Frank's rectangular metal front sits the arm at a slightly different angle than the round-front RB3447 it's sometimes confused with, so the two aren't interchangeable despite sharing a hinge screw size.

Rectangular metal frames like the Frank use a comparatively thin arm gauge to keep the overall look light, which means the arms bend out of adjustment more easily than they snap outright. A slight outward or inward bend is usually an easy fix with your fingers or a jeweler's screwdriver at the hinge, not a reason to replace the arm — reserve the swap for a cracked hinge, missing screw, or a bend sharp enough to leave a crease in the metal.

Frequently asked questions

Can I replace just one arm, or do I have to buy both?

You can order a single side if only one arm on your 3857 is broken or scratched, or buy the pair if both need replacing — either way they match the 145mm length exactly.

Are these official Ray-Ban replacement parts?

These are compatible aftermarket arms, independently produced to match the 3857's hinge and 145mm length. They aren't manufactured or supplied by Ray-Ban, just built to the same measurements so they attach correctly.

What if the arms arrive and the hinge doesn't line up with my frame?

Because each pair is listed against a specific model, in this case the 3857, mismatches are rare, but you're covered by a 14-day return window if the 145mm arms don't align with your hinge.

How do I know these arms will fit my Ray-Ban frame?

These arms are made specifically for the 3857, matching its 145mm length and Rectangle hinge design, so they attach to your existing screws and hinge without any filing or adjustment needed.