Typically, trimmer string comes wound around the head and is slowly eaten away with use. Some heads release more string automatically; others you tap on the ground. Eventually, when the spool is empty, you have to stop and wind a new one.
Check out Echo's Rapid-Loader trimmer head (left), which has locking clips that hold short pieces of plastic string. When it's time to replace them, you just pull out the old line and slide in the new—no winding necessary. Roger loves them. "I keep a handful of strings in my pocket," he says. "Within 30 seconds, I can have new ones on and I'm off to work again."