9 show a modified construction wherein the loop may be made either of plastic or wood and the bearing may constitute a stamped sheet metal plate having an indentation 25 in which the loop ends pivot the plate is attached to the inner hoop by means of round headed rivets 26 which engage the groove 22 of the outer hoop thus eliminating the need of the rib 23 in order that the hoops do not tend to spring apart when the loop is pivoted which can happen if the loop ends are excessively axially disaligned the metal bearing plates may be made as shown in fig1 to 12 by having a transverse bend 27 forming an angled mounting tab 28 so that the openings 24 of the two plates align axially and both ends 29 of the loop are also made axially aligned to pivot therein fig1 and 10a show the plate stamped from sheet metal while fig1 shows it molded of plastic referring now to fig1 and 14 a flat metal plate 30 is placed against the outer side of a plastic inner hoop so as to prevent the rivet heads 31 from breaking through the plastic hoop if the rivet holes 32 become worn thus the hoop is sandwiched between the two metal plates 19 and 30 to prevent plastic wear the plate 30 seats inside a recess 33 so that its outer side is flush with the hoop outer side.