The Craftsman 25cc Line Trimmer is a propane-powered garden tool sold by Sears for cutting weeds and clipping grass around the lawn and garden. The "25cc" represents the size of the propane engine in cubic centimeters. At the bottom of the tool, on the end of the shaft, the line trimmer head holds a straight cutting line that rotates at high speed. If the head becomes damaged, the line may no longer spin properly and the part must be replaced.
Pull the wire off the spark plug on the back of the engine for safety while you work on the trimmer.
Remove the cutting attachment shield that covers the spinning line at the bottom of the tool by extracting the two screws that hold the shield to the shaft. The screws are installed in a bracket that holds the shield on the opposite side. Save these parts for reattachment.
Twist the nut on the end of the shaft clockwise just above the line trimmer head, using a wrench. Although nuts typically twist off counterclockwise, the direction is different on a weed trimmer because the head rotates clockwise when the tool is in use. The nut's reverse threading prevents the head from flying off the line trimmer during operation.
Slide the nut back on the shaft and pull the trimmer head straight off.
Line up the new trimmer head with the shaft and push on it, sliding the nut over the threads. Tighten the new head to the shaft using a wrench.
Reconnect the cutting attachment shield to the shaft using the bracket and the two screws you previously removed.
Reattach the wire to the spark plug on the back of the engine.