We designed and made this spool holder for the ANET A3 printer. Using the threaded rod is a pretty rough rough idea and has a number of problems. Removing the printed plastic X had loosened the rod on a number of occasions. Once the rod was tightened in the wrong place and caused the Z travel to be hindered. There are three holes drilled around the main rod hole anyway so we just designed around that. they are about 3mm so i opened them out to 4.8mm 3/16 and used M5.0 x15mm screws they didn't need nuts but added for safety sake. Its simple solution, so good luck with it.