The part is design in Autodesk Fusion 360, and 3d printed on the Craftbot 2 in PLA (for now). I may switch to something less brittle later if it turns out to crack up easily in use.
It is designed to work with Homelite and maybe Black and Decker electric string trimmers. Some particular models, I don't know the number. I'm sure they make lots.
It clips in where the cap on the string reel would normally go. The reel is removed while the blade is on.