Symmetric Prusia Z-coupling

thingiverse

Combine a 5mm motor shaft with an 8mm threaded rod, aligning them coaxially while permitting slight angular movement if the rod is bent. This version provides benefits by utilizing two identical components instead of having one captive-nut side and a smooth side. Consequently, fewer part types are needed, and the bolts balance each other. As per http://things.hands.com/thing/pla_coupling/, this design avoids 'center=true' to resolve printing difficulties. The design also features rounded corners, achieved by intersecting a cube and a cylinder. Another option is to place plastic tubing over the motor shaft and secure it with M3x20 bolts. Alternatively, as suggested by Pointedstick, reduce the smaller radius hole diameter to 2.5mm and eliminate the tubing, although this may decrease the design's suspension capabilities when dealing with bent rods.