Abstract: A rail has an axially extending undercut groove of a uniform generally “C” shape in cross section and is supported by supports attached to the rail in spaced-apart relation. Each support includes a bracket and a lock member attached to the bracket for rotation and against displacement of the lock member relative to the bracket member. The lock member includes a locking cam portion, which is received in the undercut groove and has a size and shape such that it can enter the undercut groove when it is in an unlocked rotational position relative to the undercut groove and such that it frictionally engages walls of the undercut groove in a locked rotational position relative to the undercut groove and thereby retains the rail against displacement relative to a structure that supports the rail.