140mm and metal are the two figures that define arm fit on the Ray-Ban RB1971 Square, and they're what this aftermarket pair is built to. Despite the plain 'Square' name, the 1971's hinge position is specific to this model rather than shared with every square-metal Ray-Ban, so matching the model number matters as much as matching the general shape.

Metal hinges lose tension gradually rather than all at once, so a temple can go from holding an angle firmly to barely holding it at all over a year or two of normal use, without ever being visibly bent or damaged. That gradual loosening is often mistaken for a frame simply getting old, when replacing the arm — or having the hinge screw tightened — restores a firm hold without needing to guess at how many turns of the screw will fix it.