As of 2014, Cub Cadet manufactured nine different string trimmers. Some have fixed-string heads, which take a short length of string that you must replace frequently, and some have spool heads that you can rewind. Spool heads are interchangeable, and you always have the option of replacing an empty spool with a pre-loaded one to save time. In practice, however, restringing is such a simple procedure that you seldom need to change spools. Most Cub Cadet trimmers take 0.095- or 0.105-inch string, but one model -- the ST59L -- takes 0.080-inch string. Check your owner's manual to be sure you're using the correct string.
Turn off the trimmer and disconnect the spark plug wire to prevent an accidental start-up. Lay the trimmer on a flat surface with the trimmer head facing you.
Locate the two string holes in the middle of the head. Grip any old string that remains there with pliers and pull it straight out.
Cut a length of string that is about 12 inches long from a spool, using scissors. Feed one end into one of the holes and push it until you can grip the end at the point from which it exits the head. Feed the other end into the other hole in the same way.
Grip both ends of the string and pull until the section in the middle is flat and flush against the trimmer head. The two protruding lengths of string should be equal and extend only as far as the edge of the deflector, which is about 6 inches away. If the lengths aren't equal, pull the string out and repeat the procedure for installing it.
Rewinding a Trimmer Head Spool
Disconnect the spark plug wire and lay the trimmer on a flat surface so you can access the head.
Unscrew the bump knob by turning it counterclockwise. Lift off the knob and remove the string spool and spring. Put the spring in a safe place.
Wind two separate lengths of string or wind one length of split string, which consists of two lengths of string held together by a thin plastic membrane, much like electrical wire on lamp cords. If you wind the strings separately, cut two 6-foot lengths from a new spool. If you use split string, you only need one 6-foot length.
Wind separate lengths of string by first inserting one length of string into one of the holes in the hub in the middle of the spool. Wind the string in the direction of the arrow, keeping it confined to one section of the divided hub and stop winding when you have 6 inches left on the end. Wind the other string in the same way, keeping it on the other side of the divider.
Split the ends of the string about 6 inches -- if you use split string. Insert one end into one of the holes on the hub and insert the other end into the other hole. Wind the string in the direction of the arrow; the divider in the middle of the hub will automatically separate the strings. Stop winding when 6 inches are left on the ends of both strings.
Put the spring back on the spool, feed the ends of the strings through the holes on either side of the trimmer head and put the spool back into the head. Replace the bump knob and turn it clockwise to tighten it.