Craftsman gas-powered Weedwackers are equipped with two types of cutting heads: a fixed-line head or an optional trimmer head. Craftsman recommends using only brand-name line. Use the green line for cutting grass only. Red line is intended for grass and small weeds. Install black line for large weeds and small brush.
With a stiff brush, clean debris from the cutting head. Look at the cutting head and determine which holes you need to use to feed the line. Insert red and green line into the holes marked "small." Feed black line into the holes marked "large."
Insert one end of the line through one of the correct size holes in the cutting head. Feed it through to about half the length of the line. Insert the other end of the line into the other hole of the same size. Feed it through to a similar length.
Grasp one end of the line and insert it through the positioning tunnel, on the same side as you inserted that end through the cutting head hole. Do the same with the other end of the line and corresponding positioning tunnel.
Grasp both ends of the line and pull tightly in either direction. Check to see that the portion of the line between the cutting head holes is tight against the hub. Check also to see that both ends of the line are approximately the same length.
Pull on the tap button of the head to remove the spool. Set the Craftsman Weedwacker aside. With a stiff brush, clean any debris from the spool and hub.
With a tape measure and garden shears or scissors, measure and cut two strands of line, each 12 ½ feet long. Insert the end of one strand of line ½ an inch into one of the small holes on the spool. Do the same for the other strand.
Hold the spool in one hand and grasp both strands of line in the other hand. Wind the strands tightly around the spool in the direction indicated by the arrows on the spool. Stop when there are 5 to 7 inches of unwound line left on each strand.
Holding the line tight against the spool, insert the unwound end of one of the strands into one of the notches on the spool to hold it in place. Repeat this with the other unwound end. There should be 3 to 5 inches of line stretching from each of the notches.
Grasp the Weedwacker hub in one hand. With the other hand, insert one end of the line stretching from a notch through the corresponding exit hole on the hub. Take care to not release the line from the notch. Insert the other line through the other exit hole, so that the two ends of line do not cross.
Place the center hole in the spool over the drive shaft on the hub. Push the spool onto the hub so that it snaps securely. Grasp one strand of line in each hand. Pull the strands away from the head until you feel them release from the notches.
Hold one strand of line and stretch it across to the opposite side of the head. With scissors or garden shears, cut the length of the line so that it is no longer than the diameter of the head. Do the same with the other strand.