There is provided apparatus for converting between a medium tenacity yarn producing machine and a high tenacity yarn producing machine. The apparatus comprises a pulley (40) adapted to be driven by a motor after removal of a multi-disc texturing unit (11) of the medium tenacity yarn producing machine from a casing (14). A bracket (30) is securable to the casing (14) with the pulley (40) mounted to the bracket (30) by means of a bearing unit (46) such that the pulley (40) is rotatable relative to the bracket (30). The bracket (30) has one or more mounting points to which a pin spindle texturing unit (20) of the high tenacity yarn producing machine can be attached. An endless drive belt (50) connects the pulley to a drive shaft (24) of the pin spindle texturing unit (20). The diameter of the pulley (40) is greater than the diameter of the drive shaft (24), and the diameter of a drive disc (23) of the pin spindle texturing unit (20) s larger than the diameter of a disc pin spindle (21) of the unit (20).

Friction disc for a false-twist device, comprising an annular hub, on which it is possible to fix a circular race formed by a polyurethane (PU) layer and has a minimum wall thickness required for a secure interlocking fit, the hub having a circumferential support ring and a central hole, by which the friction disc is fixed on one of the shafts of the false-twist device. To ensure better dimensional and form stability over a long service life of the friction disc, the formed race fixed on the hub is ground according to a predefinable profile such that the flanks of the race have a predefinable width dimension following the grinding process, and/or in that the hub has, at a spacing from the support ring, a circumferential shoulder for abutment for the fixable PU layer, a cross-sectional width of the shoulder being smaller than a cross-sectional width of the support ring.