Replace a lost or damaged tension knob on your TC4 thread carriage using the same high-quality original parts provided by CRB. These tension knobs are compatible with both RBS System rolling carriages and the fixed-model HWS thread carriages and will support small & medium sized spools from ProWrap, Pacific Bay, Fuji and More! Compatible Models: HWS-TC4, RBS-TC4, HWS-2