A cam mechanism and method in a circular knitting machine having at least two types of knitting needles each having a master butt and at least two selector butts and including a stitch cam for engaging the master butts and retracting the needles from the knitting and tucking positions to the stitch-forming level, and knitting, tucking and welt-guarding cams movable between extended operative positions and retracted inoperative positions, and a selection device for individually selecting and moving the knitting, tucking and welt-guarding cams between the operative and inoperative positions.