Devices mountable to a rail having a recoil groove are provided. In one aspect a device mountable to a rail having a recoil groove has a rail positioner having a longitudinal length with a plurality of teeth arranged along an edge of the longitudinal length and a recoil groove insert extending away from the rail positioner and configured to be inserted into the recoil groove, a first body member having a first rail engagement surface and plurality of openings generally sized to receive the plurality of teeth and arranged along a length of the first body a second body member having a second rail engagement surface opposite the first body member, and a clamping structure operable to tighten and maintain a clamping force between the first body member and the second body member when the rail positioner is arranged in therein and that can be released facilitate installation and removal of the mounting to a rail.