Summary

The mount is changed from the "Garmin Forerunner 945/935 Quickfit Quarter Turn Bike Mount" to a smaller spacing of the holes (42.5mm) and a smaller width (15mm instead of 2mm) to accomodate the Forerunner 735XT and possibly other with the same spacing. It does not snap on the rods on the watch like the original file. Instead the rods have to be screwed into the mount, for added robustness. This can be done using a small allen key or ideally the right TORX bit.
If the holes come out too tight, drill them out with a 2mm drill bit.