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.