formed in subassembly 102 a and extend outwardly therefrom into aperture 106 a second plurality of rigid locking teeth 104 b are formed in subassembly 102 b and extend outwardly therefrom into aperture 106 referring to fig3 a 3b and 3c each subassembly 102 comprises a u shaped housing comprising a first lip 110 an opposing second lip 140 each subassembly 110 further comprises a first side wall 120 interconnecting a first end of first lip 110 and a first end of second lip 140 and a second side wall 130 interconnecting a second end of first lip 110 and a second end of second lip 140 a bottom 150 interconnects from lip 110 read lip 140 first side 120 and second side 130 a plurality of locking teeth 104 extend outwardly from bottom 150 side wall 120 and side wall 130 each comprises a height 122 where side wall 120 and side wall 130 each connect to first lip 110 and a height 124 where side wall 120 and side wall each connect to second lip 140 in certain embodiments height 122 is greater than height 124 in these embodiments side walls 120 and 130 comprise a trapezoidal shape in certain embodiments side wall 120 first lip 110 side wall 130 and.