sake of clarity fig8 a is a perspective view of the knob cam portion 2000 of fig1 showing a knurled portion 2330 the remaining parts are as described in the foregoing fig8 b is a perspective view of another embodiment of the knob cam portion 2000 having a plurality of separated rib portions 2340 for ease of gripping and rotating the remaining parts are as described in the foregoing fig9 a is a side elevational view of a further embodiment of a knob cam portion 2000 of fig1 having an annular bottom surface 2350 here the cam 2120 is shown having respective engaging edge 2121 and uppermost edge 2127 by providing clamping force the tiles will self level guided by the datum plane created by the bottom annular portion 2350 of the knob cam the knob cam 2000 can be reused the remaining parts are as numbered and described in the foregoing fig9 b is a top elevational view of the knob cam portion 2000 of fig9 a showing the cam 2110 and the cam 2120 together with the pairs of radial valleys 2115 and 2125 the pairs of radial valleys facilitate seating and locking of the blade portions 3110 and 3120 during operation fig9 c is an enlarged frontal section of a portion of the cam 2120 showing a close up view of the teethed stepped radial valleys 2125 each of the radial valleys 2125 has a generally scalloped shape and.