This is the direct replacement part for the B&D Grass Hog model NST2018.  I love that trimmer as it is easy to use and I don't have to fight with a gas powered trimmer and all the problems involved with using one.  This replacement spool directly fits onto the trimmer and is easy to change.  The trimmer is designed to automatically feed the trimmer line and I didn't want to mess with rewinding line onto the old spool.