pin 20a secured to base plate 14 is received within the mounting pin receiving void 16a although not visible in this figure a similar series of voids 16b d exists for pins 20 b d these series of pins 20a d and associated voids 16a d comprise the fulcrum means discussed below it will be observed from the figure that mounting pin receiving void 16a comprises an opening 28a in the lower portion thereof of a size and shape which permits head 21a of pin 20a to be projected therethrough the void 16a further includes a forward portion 26a which permits the forward portion 52a of head 21a to be slidably received and frictionally engaged therein it can also be seen in the figure that the clamping plate 12 has been moved slightly rearwardly relative to base plate 14 as illustrated the forward portion 52a of head 21a on pin 20a has just begun to be received within the forward portion 26a of receiving void 16a as mentioned above once the forward portion of head 21a has been received and frictionally engaged in void 16a plate 12 and plate 14 are releasably secured this frictional engagement between pins 20a d and the clamping plate 12 forms a fulcrum point permitting the blade to be clamped into position between the base and clamping plates as mentioned in the preferred embodiment the fulcrum means comprises a series of mounting pins 20a d secured to bottom base.