These x-ends don't hold x-rods, they hold a single 20x20 extrusion.This particular version uses lm8uus and a 3 hole delrin nut for the lead screw.both ends have an integrated bolt holder meant to interface with a z-endstop held in the lower part from http://www.thingiverse.com/thing:28425By the way these are intended for 605zz idler bearings, you'll have to enlarge the hole either before or after printing if you intend to use 608zzs.