Abstract: A thread cutting device of a sewing machine comprising a groove defined in a sewing machine, the groove extending back and forth and having an opening at a back end thereof, a plurality of thread cutting blades having inclined grooves along which each piece of thread cutting blades can be broken off every given interval, wherein a tip end of each thread cutting blade is disposed to across an intermediate portion of the groove, and the each thread cutting blade is fixed to the sewing machine by way of a detachable fixing means.

Abstract: A thread guide holder device comprises a thread guide holder which is mounted on a spool stand base and has thread guides each for guiding a thread therethrough, wherein the thread guide holder is mounted on the spool stand base by way of damping materials. As a result, it is possible to restrain the oscillation of the thread guide holder during sewing operation so as to smoothly draw out the threads through the thread guides of the thread guide holder and consequently prevent irregular stitches and restrain an eye-offensive oscillation of the thread guide holder.

Abstract: A stitch balancing thread tension device for a sewing machine, the body of which is inserted into the opening portion of the sewing machine body, wherein the thread tension device body for supporting a stem on which a pair of tension discs are fit, comprises a projecting portion which contacts the outer side surface of the sewing machine body and pawls which are retained at the circumferential edge of the opening portion by the inner side surface of the sewing machine body for clamping the sewing machine body therebetween. The pawls are elastically invaginable into the thread tension device body to release the sewing machine body from clamping. Since the thread tension device can be attached to or detached from the sewing machine body in one-shot operation, the operability is remarkably improved in efficiency.