RB2447NM Round pairs a round metal front with 145mm metal arms, longer than the 140mm size used on most of Ray-Ban's round metal lines. This aftermarket pair matches both the extended length and the round curve, so the temple follows the front's arc into the hinge rather than sitting straighter like a square-frame arm would. Confirming the 145mm figure against the model code is worth the extra minute, since it's easy to assume a round Ray-Ban arm defaults to the more common 140mm length.

Round metal sunglasses like the 2447 put continuous curved tension through the arm rather than a single straight bend, which is part of why the hinge screw tends to loosen gradually rather than all at once. A gentle periodic tightening keeps the round shape sitting evenly rather than drifting to one side. Measuring the old arm before ordering, when it's available, is a simple way to double-check the 145mm figure without relying on memory.