the release lever 154 can rotate around the pin 190 that is fixed relative to the clamp support base 152 in the example shown the release lever 154 can rotate about ninety degrees with the pin 190 between the first and second closed positions other configurations are contemplated the locking portion 186 of the release lever 154 will now be described in greater detail the locking portion 186 can have an engaging surface 196 that collectively includes a first concave surface 200 a cam surface 202 and a second concave surface 204 in one example the first and second concave surfaces 200 and 204 can substantially match the outer profile of the first and second locking members 156 and 158 respectively a smooth arcuate transition can be provided along the engaging surface 196 from the first and second concave surfaces 200 and 204 to the cam surface 202 the smooth arcuate transition can facilitate a smooth and uniform engagement of the release lever 154 with the first and second locking members 156 and 158 during rotation of the release lever 154 between the first and second closed positions with particular reference now to fig8 with the release lever 154 in the first closed position the cam surface 202 of the locking portion 186 is substantially aligned for engagement with the first locking member 156 and the second concave surface 204 is substantially aligned for engagement with the second locking member 158 in this regard the cam surface 202 can operatively urge the first locking member 156 at least partially into the first slot 160 in the first closed position.