they can be adjusted slightly. I think they can go up or down 1 shell size...but not both, for example you can mount them for a 27 and they can go up to a 28, but can't go down to a 26 with the same mount. It's kinda hard to explain, basically there's a screw type thing on the arms that attach the base plate to the release part on the heel piece that can be screwed in or out to adjust, but only goes out one size so you can either start it with it all the way out or start it with it all the way in.