Abstract: 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).