distal edges 36 of the flanges 30 rotate into the track 18 just behind the slot opening 40 the bevel 37 leading to the distal edges 36 of the flanges 30 prevent the distal edges 36 from catching on the open edges of the slot 40 as the flanges 30 rotate past these edges as the flanges 30 rotate toward 90 degrees contact occurs between the flanges 30 and the track 18 at two different points as the distal edges 36 of the flanges 30 rotate they contact the interior of the track 18 causing an interference fit simultaneously the second edges 38 rotate and contact the open edges of the slot 40 this also causes an interference fit consequently as the brake head 22 rotates an interference occurs between the structure of the track 18 and both the distal edges 36 and the second edges 38 of the flanges 30 this wedges the brake head 22 in place and prevents the brake head 22 from being moved in the track 18 as the brake head 22 is being rotated in the track 18 to cause an interference fit yet another braking action is occurring as the brake head 22 rotates in the track 18 the.