This allows you to connect two ends of an ANSI MXL sized timing belt together. You can use this to take a length of belt and turn it into a loop.
It's designed to fit very snugly on the belt, so you may need to use a small flathead screwdriver to push the belt into the coupler. It provides a very solid joint.
It would be nice to make this parametric in OpenSCAD. I needed to knock something out quickly for a robotics project, so I did this in SolidWorks as seen in the attached .sldpart file.
I printed this on my Replicator sliced at 0.25mm layer height. I got the most consistent results when I oriented the model so the open side (the side you press the belt into) was facing up. I normally print raftless, but in this orientation there is very little surface area in contact with the HBP, which was giving me some issues. I had much better success once I printed with a raft.