the mechanism these means are a circular array of bearings 66 an annular bearing race 68 and a yieldable resilient annular element 70 the specific details of these components and their operative association with the mechanism will be subsequently explained said another portion of the mechanism illustrated in the drawing figures comprises a tubular member 72 and a locking cap 74 tubular member 72 extends longitudinally of the mechanism along axis 38 and the end of tubular member 72 opposite the end of shaft 42 i e the right end as viewed in fig4 and 5 is provided with a pair of diametrically aligned holes 76 through its sidewall to provide for attachment to hinge member 20 as viewed in fig1 and 3 attachment is made by means of a pin 78 passed through the holes 76 and an aligned hole in hinge member 20 with means being provided for keeping them connected tubular member 72 is also provided with a transverse end wall 80 at the end thereof which is toward shaft 42 i e left end as viewed in fig4 and 5 this end wall 80 is provided with a central circular hole 82 concentric with axis 38 and through which the distal right hand end of shaft 42 passes hole 82 provides clearance for the distal end of the shaft the outside diameter of tubular member 72 is of circular shape and is provided with a screw thread 84 which is generally axially co extensive with the region of end wall 80 locking cap 74 comprises an axially extending sidewall 86 and a transverse end wall 88 the end of cap 74 which is toward tubular member 72 is open and is provided.