This replaces the poorly printed original. It uses set screws for smooth rod assembly. Extruder mounts 1/2" higher for added build height. Eliminates misalignment of feed and smooth rods. Includes adjustable Z endstop holder. Designed for (8) standard 24mm linear bearings or (4) 45mm. Idler now has an X belt tensioner included. My I3 kit had terribly printed x carriage parts. Feed and smooth rods crossed like chop sticks causing a massive bind in the Z Axis. End pieces had to be hammered onto smooth X rods making alignment impossible. With these parts you simply slide parts together and install on printer. Then you tighten the set screws on the smooth rods and perfect alignment is achived. Install new Z Endstop Holder and readjust Z height.