This is a jig for drilling out 12mm wheel hex to a 5mm bore for when a hex wont seat all the way. Not all wheel hex accommodate every axle, some have a 5mm step to them. This jig helps keep the drill bit centered while you bore it out.
Push Plastic PETG
PLA would be fine I just thought PETG might hold up a bit longer. After a few uses so far it doesn't show much wear at all.
Instead of 100% infill you can use multiple perimeters