Stihl, a German chainsaw innovator and power tool manufacturing company, makes, besides professional-grade chainsaws, many types of yard tools designed to keep yards looking their best. One of the company's most popular consumer-grade products is a string trimmer, also commonly known as "weed eater." The string trimmer uses nylon string at the trimmer head (at the bottom of the shaft), which rotates rapidly, effectively turning the nylon string into blades. Many Stihl trimmers have interchangeable heads for varying purposes, such as edging and mowing. To attach a new head, start by removing the head that's currently on the trimmer.
Turn off the trimmer and lay it on its back, so that the trimmer head at the opposite end of the shaft from the engine is pointing up.
Insert a screwdriver into the hole on the right side of the gearbox to block the shaft from rotating.
Twist the entire head assembly clockwise, while applying pressure with the screwdriver, to unscrew the head from the mounting screw. When it breaks loose, pin it to remove it.