when i order them, they make me order a front and rear specific unit. when i get 'em, i open the one that says "front" on the box, and put it up front. then, i take the one in the box labeled "rear" and put it out back. I'll bet there's something on the arms, but to be honest, i don't have one in front of me. There's no extremely obvious difference.

Some avid v-brakes are interchangeable; others aren't. Quite frankly, i don't get it. I just do as i'm told.

-rob