Abstract: A fluid operated clamping mechanism comprising, a clamp body having end closure members thereon, a chamber formed within the clamp body, a piston mounted within said chamber for back and forth movement therein, said piston including a magnet associated therewith, a piston rod connected to said piston at one end and a second end of said piston rod extending through the top of the clamp body, a clamp arm being connected to said second end of the piston rod, a first fluid port near said bottom closure member, a second fluid port near said top closure member, said first and second ports being adapted for introduction of a pressure fluid on a first and second side of said piston to thereby cause back and forth movement of the piston rod and which thereby moves the clamp arm between its clamped and un-clamped position, said clamp body containing at least two external surfaces thereon which run lengthwise in the same direction as the piston rod, each of said surfaces containing a different specially grooved slot gen