mounted on hollow receptacle portion 67a and cover portion 66 is mounted on hollow receptacle portion 67b cover portion 65 functions in a manner similar to that described for cover portion 5 of fig1 and thus will not be repeated here the cover portion has a plurality of indentations 68 having side walls 69 and 70 and an apex 71 the apex 71 lies along a radius originating from receptacle axis 72 each indentation 68 has a triangular cross section defined by the side walls 69 and 70 that open toward the cover portion 65 the indentations of cover portions 65 and 66 form a closed area having a square cross section for gripping tubing 73 held therebetween bolts 74 and 76 extend through cover portions 65 and 66 respectively bolt nuts 77 and 86 engage bolts 76 and 85 respectively and upon tightening urge cover portions 65 and 66 together thereby gripping tubing 73 between the cover portions similar bolting arrangements not shown are located symmetrically between the other indentations disposed on the cover portions as may be apparent the structure of fig1 a provides for the gripping of varying sized tubing thus for larger sized tubing the cover portions will be held further apart whereas for smaller sized tubing the cover portions will be held closer together collar 78 is slidably mounted on receptacle portion 67a and locked in place by set screw 79 similarly collar 80 is.