also corresponds to the position of edge 36 relative to leading edge 34 of catch shoulder 33 edge 81 extending substantially transversely to arm 71 is followed by an obliquely extending edge 82 which in turn is followed by an edge 83 extending substantially parallel to arm 71 edge 83 terminates directly at the inner longitudinal side 84 of catch shoulder 74 the spacing between edge 81 and the inner longitudinal side 84 of catch shoulder 74 is understood to be the amount a 39 which is the height of retaining shoulder 80 a leaf spring 85 extending substantially horizontally is provided in spaced relationship with a cutting knife 79 with thread catcher 70 in the cutting or rest position spring 85 along with the underside of retaining shoulder 80 forms a thread clamp 86 for bobbin thread g the free end of leaf spring 85 is spaced from the inner longitudinal side 84 of catch shoulder 74 by a distance which exceeds the maximum possible thickness of the needle thread at the end of a sewing operation the sewing machine is stopped by means of a positioning motor known per se with the needle 6 in the lowermost position this is followed by half a revolution of arm shaft 5.