A square metal front like the RB3648M's needs a temple arm cut to the same specification: 140mm in length, metal construction, built for this exact Ray-Ban model rather than a similar-looking square frame. Anything off on length changes how the arms sit behind the ear and throws off the balance against the square front. An aftermarket arm that misses either the 140mm mark or the metal finish usually shows up as a visible gap at the hinge or an uneven lean once the glasses are on.

Square metal frames tend to open to a wider angle than rounder styles, which puts more repeated strain on the hinge screw than on the temple itself. If an arm has started to feel loose at the pivot while the front is still solid, that's usually the hinge wearing, not the metal failing. A compatible replacement arm resolves that looseness directly, and there's no reason to replace the front along with it if the square shape and lenses are still in good condition.

Frequently asked questions

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 3648, mismatches are rare, but you're covered by a 14-day return window if the 140mm 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 3648, matching its 140mm length and Square hinge design, so they attach to your existing screws and hinge without any filing or adjustment needed.

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 3648 is broken or scratched, or buy the pair if both need replacing — either way they match the 140mm length exactly.

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

A new 140mm arm includes its own hinge barrel, so if the wobble is coming from worn threading on the arm side of the 3648, replacing it usually restores a snug, tight fold.