I used PLA to make this. You may want to increase the height which is on this line (h=1) : cylinder(r=spool_hole_diam/2 + 4, h=1) to make it a little sturdier. I am planning on making a bunch of these so I took it down to h=1 to save on material and print time. Someone had a suggestion to use a rubber band to string the two halves together if they pop off. I did not have any issue with them popping off.