Print at .2mm 20% infill. I used PLA which seems to work well. You will need some spring wire. I have used both .024" and .031" spring wire in this former and they both work well. In the US you can find spring wire, stainless steel cut in 12" lengths from McMater Carr. ($17 US plus shipping) I also bought a 1lb spool of wire from Amazon - about $9 U.S 400 feet. There is a small hole at the beginning of the threads on the mandrel. Most of the time the hole fills up and has to be drilled out. Use about an .030 bit but the size doesn't matter too much. This hole is just to secure the wire in place. 1. Screw the mandrel into the sleeve all the way. Align the sleeve slot with the small hole. I would suggest printing the mandrel in white and using a black marker, mark the hole. It will be easier to find the hole this way. 2. Insert the wiring into the hole as far as it will go. 3. Begin unscrewing the sleeve from the mandrel. Continue until the sleeve is completely separated from the mandrel. NOTE: There will be springback as you unscrew the sleeve. You can search SPRINGBACK with your favorite search engine for lots of information. Basically there is enough tension in the wire that even though we are forming around a 7 mm mandrel, once the sleeve is removed the wire will relax slightly and springback to a larger diameter. 4. Using side cutters or something that can pry the starting end out of the hole so that. Then unscrew the spring from the mandrel. Since the springback enlarged the diameter it will be easy to remove. I have included Fusion 360 Design files and a .step file so you can modify this. For the threads I used a square coil. the threads on the mandrel are purposely made a little smaller than the treads on the sleeve. There seems to be some issue with the pitch holding dimensions - the further you inserted the tighter the fit. For the length provided in this design it seems to mate well.