clamp arms 28 are pivotally secured to the body portion of the clamp along a first rotatable shaft or rod 29 with each clamp arm including a window interface 31 that pivotally attaches the clamp arm to the upper window 24 an actuator 30 effectuates rotational movement of the clamp arm relative to the clamp base as perhaps best seen in fig8 the illustrated clamp arms 28 extend around the rod 29 each arm 28 includes a relatively long window interface portion 28 a on one side as illustrated the top side of the rotatable shaft 29 and a relatively short relative to the window interface portion return portion 28 b on the opposite side the actuator 30 includes a rotable shaft 30 a that extends parallel to the first rotatable shaft 29 the actuator shaft includes an offset portion 30 b rollers 33 are rotatably mounted on this offset portion 30 b of actuator shaft 30 when the actuator 30 is rotated and moved from the clamp open position of fig5 to the clamp closed position of fig6 the rollers 33 move along an arcuate path in contact with the return arm portion 28 b the positions of the rollers relative to the arm in the clamp open position and clamp closed position are shown in fig8 and 10 respectively this movement of the rollers 33 applies a bending stress against the return portion of the clamp arms 28 a and tends to separate the interface 28 a and return portions 28 b of the arm 28 the resilient properties of the clamp.