ok, the metal plate with the gear goes in place of the regular plate on the Kenmore--then you choose the buttonhole cam you want and dial it into the oblong gold selector making sure the size you want shows in the window--then use the screw on the back of the selector plate to screw it tightly onto the machine. The monogram attachment has an attached metal plate and snaps in place of the regular plate just like the buttonhole one does and the letter cams are dialed in only just barely to start. And Kenmore that has the snap in plate and a screw hole at the back of the machine will work. Mine is a 158.1941 You can probably go on line and find the instruction manual to the monomgrammer---I sold mine after I got my Viking 500 with built in monograms but I could scan and email you the directions for the buttonholer if you need them.