This slot cover was tested on the rails used in an Anet A2 printer. A picture of the rail tested is above.
On the Anet A2 this cover is useful for being able to run the x-axis end-stop wire separately from the x-axis belt. You will need to print about 30cm to cover the slot nicely. I printed 2 x 200mm lengths which took less than half an hour.
The default size is 100mm long however this can be customised by editing the SCAD file, using the Thingiverse customiser or by stretching it out in your slicer.
CC-BY-SA license - https://creativecommons.org/licenses/by-sa/2.5
This design was tested with PETG which is known for bad bridging/overhangs so ABS and PLA should work well, if not better.
Trimming and Fitting
Depending on how well your printer works you may have to trim about 2.5mm off one (or each) end as the ends tend to get bulging artifacts that may make them not fit easily.
If you are having trouble getting it to clip try starting at an end and clipping that first.
Trimming can be done with scissors.