rivet 33 and the other end is attached to rivet 33 39 to hold the two mating portions 29 31 tightly together in additon wedge portion 29 has a longitudinal groove 35 extending approximately one half its length a portion 31 has a longitudinal groove 36 which extends the length thereof and is internally threaded grooves 35 36 are disposed for receiving a threaded rod 37 when portions 29 31 are mated rod 37 has an end slot 39 therein for receiving a screwdriver not shown to turn the rod when rod 37 is turned in a clockwise direction the rod limits against the bottom of groove 35 and wedge portion 31 advances upward relative to portion 29 thereby increasing the thickness of the wedge 27 and when rod 37 is turned in a counter clockwise direction wedge portion 31 moves relative to portion 29 thereby decreasing the thickness of the wedge 27 by rotating the rods to vary the thickness of each wedge post 23 is moved laterally relative to the sides of enclosure 11 thereby plumbing the post the spring 34 wrapped in groove 32 and encircling wedge portions 29 and 31 serves to keep the wedge portions together and to effectuate movement of said wedge portions relative to each other when threaded rod 37 is turned preferably the enclosure 11 including the four sides 13 15 17 19 is molded in one piece from a suitable high strength plastic the enclosure may be of desired cross sectional and length dimensions selected for the.