The hole for the sheet is mechanically de-burred to ensure the sheet does not abrade or chafe. The item is then tumbled in abrasive medium to remove all external sharp edges and give a satin finish.
The part is designed to be a push fit onto the boom tube. If it is too slack use pliers or a vice to gently squash the hole to an elliptical shape until the grip is good. If the grip is too tight use a small round file to remove some material from the inside of the part until it is a good fit. When you are sure the part is properly positioned on the rig and aligned symmetrically use a spot of cyanoacrylate glue to lock in place.