A clamp for gripping an elongate member comprises a mounting block having locating structures defining a desired position for the elongate member. Primary and secondary clamping yokes are each movable relative to the mounting block between a closed position, in which the clamping yoke engages an elongate member in the desired position, and an open position. A latch retains the primary clamping yoke in the closed position, and a force-transfer arm is effective between the primary clamping yoke and the secondary clamping yoke for retaining the secondary clamping yoke in its closed position when the primary clamping yoke is in its closed position.