you can add this to the printrbot so the z rods become connected, they restrain the screws by keeping them vertical, this works better with a screw isolator like this: http://www.thingiverse.com/thing:40272 to avoid any problem caused by a non-straight screw or any misaligment. i designed this for a 9.5mm horizontal rod i had lying around, i am providing the files so you can change the diameter to the one you prefer, or you can ask and i will upload it for different rods. this works with the printrbot plus V1, i'm think they didn't change the dimensions between the rod and the screw in the V2 or in the non-plus, but i'm not sure.