1. Reinforced metal at the bottom for improved durability. 2. Anyone can easily rewind cords. 3. Safe and secure nylon cutter is much easier! 4. Can be installed on most grass trimmers (compatible with 26cc to 35cc engines) 5 rotations when the bottom is hit to the ground when the cord is extended. 6. Nylon cord allows you to use it safely near concrete or walls.