This things WORKS and works well. I use it every week and this latest design has been in use for most of this year without breaking. I believe is used 6mm round line cut into 8-9" lenghts. Load the line from the inside and hook the center on the innner hook. one load usually lasts me one full yard trimming and edging on my driveway. This will directly replace the stock head and fit without modification.

print slow and ensure good layer adhesion, use TPU