For those having trouble getting the axle shafts and differential sun gears to mate: after much trial and error I finally have created a sun gear that mates perfectly with the axle shaft every print. The square key has ben carried all the way through to eliminate printer trouble with the lip in the middle where the square key meets the screw throughole. A countersunk M3 screw still works perfectly to fix the two together.Print in ABS at 90% infill with no support or raft. Orient with the teeth up.