with reference to the side face 41 of the lower entraining member 31 of fig4 and extends across the space beneath the gap 45 the cutting edge 49 is or can be substantially vertical see fig3 if desired the knife 47 can be produced as a separate part which is separably or permanently affixed e g welded to the leg 27 of the thread guide 21 this may be desirable if the knife 47 is to be installed in an existing overlock sewing machine if the thread 51 is not broken it extends from the source 53 through the two guides 19 of fig2 and along the outer side of the leg 27 prior to being trained over the shaft 38 of the tensioning device 37 and entering the deepmost portion 24 of the slot 23 in the leg 27 at such time the flats 35 of the entraining members 31 are substantially horizontal the thread 51 then extends at b in parallelism with the axis of the shaft 33 toward and outwardly through the deepmost portion of the slot 23 in the leg 29 and thence toward and through an eyelet 30 which is shown in fig4 the location of the eyelet 30 is or can be such that the portion of thread 51 between the deepmost portion of the slot 23 in the leg 29 and the eyelet 30 is substantially parallel to the outer side of the leg 29 see fig4 that portion of the thread 51 which advances beyond the eyelet 30 is engaged by a hook or shuttle not shown of conventional design if the disc shaped looping members 31 are rotated in a clockwise direction.