145mm is the one number that has to match on a Ray-Ban RB3647N temple arm, and it's what this aftermarket pair is cut to. Beyond length, fit depends on the hinge cut lining up with the RB3647N mold, which is specific to this model rather than shared across the wider RB3600 range. Confirming the model number on the arm you're replacing, rather than judging by eye, is the safest way to be sure a replacement will seat correctly.

On most Ray-Ban frames, a temple arm is the single point most likely to fail before the front does — a bent hinge, a snapped tip, or a stripped screw hole, while the lenses and front frame are still in good shape. Replacing the arm alone, rather than the whole pair, is the cheaper route whenever the damage is limited to one or both temples. It also makes more sense than retiring a sound front frame over a single broken part.

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 3647 is broken or scratched, or buy the pair if both need replacing — either way they match the 145mm length exactly.

Do I need a specific screwdriver to attach these myself?

You'll need a small eyeglass screwdriver, typically included in basic repair kits, to remove the old hinge screw and attach the new 145mm arm to your 3647 frame — the whole swap usually takes under five minutes.

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 3647, mismatches are rare, but you're covered by a 14-day return window if the 145mm arms don't align with your hinge.

My hinge feels loose — will new arms fix that, or is it the frame that's worn?

A new 145mm arm includes its own hinge barrel, so if the wobble is coming from worn threading on the arm side of the 3647, replacing it usually restores a snug, tight fold.