The spool head on a Ryobi trimmer keeps the line inside the spool. The spool head also helps regulate the amount of string that comes out when you bump the automatic feeder. This plastic head will get worn out over time or quickly if you trim over rough, rocky areas. You should always replace this piece if it is worn out and do not try operating the trimmer without this head properly attached. Only replace this part with a certified Ryobi replacement part.
Turn off the trimmer and let it cool down for a few minutes. Flip the trimmer up so you can work on the head.
Hold the outer spool with one hand and with the other turn the centre knob counterclockwise.
Pull the outer spool off the trimmer head. Pull the inner reel and spring out from the spool. Keep the inner reel and spring together and discard the spool head if it is worn out.
Reinstall the inner reel and spring back into the new spool head. Hold the spool head over the centre of the trimmer head. Push the spool head down and turn it clockwise to tighten it to the trimmer head.
When removing the spring and inner reel, make sure these pieces stay connected.