This spool cap is a genuine MTD replacement part for line trimmers, otherwise known as string trimmers, weed eaters, weed whackers, or brush cutters. Line trimmers are used to trim the edges of pathways, trees, shrubs, and manicured greenery. The function of a spool cap for a line trimmer is to encase the bottom of the line spool to protect the spool from unraveling out of its housing.A spool cap might need to be individually replaced if the spool in the line trimmer unspools from its housing and cannot be contained; this likely means that the spool cap was lost, misplaced, or suffered from some form of damage that rendered it ineffective, such as cracks, chips, tears, or erosion. This damage can simply occur from long-term overuse or general wear and tear. A replacement spool cap should be ordered and integrated into the line spool before using the line trimmer appliance again. Remember to always wear gloves when handling, repairing, and operating outdoor equipment. This spool cap is compatible with the following brands: MTD and Troy-Bilt. This part sold individually.