surface 95 of the bushing 91 to the rear surface 102 of the flange 98 is substantially equal to the height of the support member 52 from the visible surface of the central member 51 to the visible surface of the base 54 furthermore the aperture 99 is formed so as to be substantially directly aligned with the aperture 56 when the pins 93 and 94 are in the holes 96 and 97 all of the units described to this point are mounted on a plate 103 to be attached as a preassembled structure to the arm of a sewing machine the plate 103 has a rectangular opening 104 and a threaded hole 106 along side it the rectangular opening 104 is shaped to fit the end 105 of the bushing 91 and the threaded hole 106 is located to be aligned with the apertures 56 and 91 to receive a machine screw 107 to hold one end of the mounting bracket 49 and the bushing 91 firmly in place on the plate 103 the other end of the bracket 49 is held in place by another machine screw 108 through the aperture 58 in the base 57 and screwed into a threaded hole 109 in the plate 103 thus only two screws 107 and 108 are needed to hold all of the parts in place on the plate 103 when these parts are so assembled the dog 23 is in position to slide within a slot 111 the presser bar guide 18 of which the dog 23 is an integral part is machined of metal and in order to minimize friction the slot 111 is defined within an elongated border 112 of low friction material such as delrin or celcon similar to the bushing 91 and.