a clamp mechanism for clamping the edge of a printed circuit board between the side walls of a slot in a wall of an enclosure for housing the board in parallel spaced relationship with other boards . the mechanism comprises an elongated element of resilient material having corrugations whose crests are at regularly spaced positions along its length . an actuator coupled with the elongated element for relative longitudinal motion therewith is provided with riser elements spaced like the corrugations and positioned so as to move on such relative motion into engagement with the crests to effect the required clamping action . the riser elements are in the form of rollers to minimize functional resistance to operation . a spigot arrangement on a lever 75 for operates the mechanism which provides positive locking of the board when clamped .