elongated and centrally positioned extends through the flat upper surface 66 the head 64 includes a track 68 a first mounting member 70 and a second mounting member 72 as shown in fig8 the track 68 has a substantially uniform base 74 which defines the bottom of the track 68 the base is sized and shaped to fit on the upper flat surface 66 of the shank 62 between lips 67 the bottom of the track 68 is preferably fixedly attached to the upper flat surface 66 and or lips 67 the base 74 also defines an inner slideable surface 92 which is preferably flat and extends the entire length of the base 74 extending upwardly from each side of the base 74 is a wall member on one side of the base 74 there is a first wall member 76 and on the opposing side of the base 74 there is a second wall member 78 the wall members 76 78 are substantially mirror images with respect to one another as they are positioned on the base 74 of the track 68 together base 74 and first wall member 76 define a first outer wall surface 80 and base 74 and second wall member 78 define a second outer wall surface 82 first wall member 76 also defines a first top surface 84 and second wall member 78 defines a second top surface 86 first top surface 84 and second top surface 86 are preferably both flat and in the same plane as one another.