A keyed mounting arrangement for a light or other object mountable on a mounting rail having a keying feature may comprise a body containing operating elements; a clamping arrangement including clamp members on the body for clamping and releasing the mounting rail; and a keying member removably disposed in a recess located on the body in a predetermined location and having a keying feature that engages the keying feature of the mounting rail when the body is clamped to the mounting rail. Where the object is mountable on mounting rails having keying features of different sizes and shapes, the keying member may be selected from a set of keying members for having a keying feature of a size and shape that corresponds to the size and shape of the keying feature of the mounting rail.