FlSun Delta strong and simple carriage (GT2 belt)

Most of the carriages available for delta's with linear rails have little posts around which the belts get looped to then lock onto themselves.

I got fed up with (1) these posts breaking off when tensioning the belts or after a few days of use and (2) trying to pre-tension the belt properly when installing and failing miserably.

It looked like https://www.thingiverse.com/thing:818954 would fit the bill. However, the belt would slide out of the slot too easily, so I decided to make my own d