This is an adapter for the Cygolite Expilion OEM helmet mount to convert it to mounting on a GoPro. I created it so that I could mount my light using the GoPro mount under my Garmin computer mount rather than having something extra clipped onto my handlebars.
Just unscrew the bolt and nut from the helmet mount, and reuse them to attach the clip to this adapter.
I tried printing with and without supports, as well as with and without a raft and had similar results, but that may vary depending on your printer and material.
I used PET-G filament at 100% infill for strength.