Cap for UM2 slider blocks

I just built a Ultimaker 2 clone, and there are issues (expected).
One is the bottom 6mm rod always pops out of the sliding block.
This cap solves that problem, just fasten this cap on the sliding block and slide the 6mm rod through. I used PETG.

Used this thing as a template.
http://www.thingiverse.com/thing:1146888