The Black and Decker String Trimmer Auto Feed System Replacement Spool eases the work of hand winding. It features a 0.065 diameter line and utilizes centrifugal force to automatically feed the cutting string while eliminating bumps and hitches. This product comes with an ample supply that will last you a while. It has a multi-purpose use by being compatible with a variety of string trimmers. The item is ready to use so there is no assembly needed other than attaching it. It fits the following Black and Decker string trimmer models: GH400 GH500 GH600 GH610 GH900 GH912 ST6600 ST7000 ST7700 CST1000 CST1200 CST2000 MTC220 MTE912 NST2018 NST1118 NST2118 LST220 LST300 LST400 LST420 and LST136.