EDIT - 15.3.2016:
I have read feedback that might aid in selecting which variant to print. The tight variant works well for the stock steel bearings, while the oversize variant is great for plastic bushings like the IGUS bushings.
These blocks are made to replace the stock aluminum bearing blocks that some printers come with to reduce the weight
The blocks with the low flange on one side is for the Wanhao Duplicator i3 X-axis. they are made to prevent the belt rubbing on the block, like it does with the stock aluminum blocks.
The oversize blocks have a slightly larger bearing hole diameter to ease bearing installation if you don't have a press.
Stock-bearing01.STL - Tight bearing hole
Stock-bearing02.STL - Tight bearing hole Wanhao block
Stock-bearing03.STL - Oversize bearing hole
Stock-bearing04.STL - Oversize bearing hole Wanhao block