The Prusa i3 is really a great design. The only thing I have problem with is the way the x belt is tensioned. Since the x smooth rods are not clamped in the x end, the belt tension is actually on the z smooth rods. I probably have some low quality smooth rods but for me it tends to bend the z smooth rods so I cannot put much tension on the belt. The ugly x-end you see on the picture is the result of this lack of tension on the x belt.
This part is a quick and dirty upgrade which reuses all the original part and just adds a plate to put the load on the x axis smooth rods instead of loading the z axis.
It uses 2 M6 bolts and nuts. The M4 nut in the middle is the original one from the Prusa i3 idler holder. The bolt holding the idler holder in the x end is removed.