This is a spool retainer for your trimmer. You may also know this part as a bump knob. It is a right-hand thread screw to remove and attach to your trimmer head. Inside the spool housing, it holds the spool with the cutting line. It also is acts as a protection bumper to advance the line from the spool without damage. This part is considered a wear and tear part on your trimmer as it is constantly replaced.
Installation Instructions
Fred from Shevlin, MN says,
Spool retainer was worn and could not be removed from overheated spool assembly.
I used a pliers to hold shaft steady and a wrench to remove the inner bolt. I replaced the spool assembly and installed the new spool retainer. This took about ten minutes to fix once the problem was ...read more