Have you ever been out in the back forty with your string trimmer and run out of line? The String Caddy clamps to the shaft of your string trimmer and holds up to 16 of extra line. This can be a real time saver, as you dont have to walk back to wherever you started to get more line when you run out. Simply cut the length of line you need, then coil it up and pop it in! The friction it applies trying to uncoil itself is what holds it in!