Brace to keep bottom end of the smooth Z-Axis rods from popping out of the metal stepper motor mounting bracket. The mount is barely .5mm thick and I noticed that mine would come out with the Z-Hop when moving around prints.
You will need to print one as is and mirror the brace to produce one for the opposing side.
.2 layer, .8 shell, .6 top/bottom
80 speed, ABS 250 nozzle, 100 bed