The spool cap on my Worx WG150 battery powered trimmer broke. Replacements are readily available online, but I didn't want to wait to get one in the mail, so I printed one instead. It fits great and worked great too.
UPDATE: The first one broke along one of the print layers, so I printed the next one rotated 90 degrees for added strength. It's holding up much better so far.
I printed at .3 because it doesn't have to be pretty, but pretty much anything will work.
Generic, I used ABS, but I don't see why PLA or PETG wouldn't also work.