The stock J-hook that comes with the GoPro (and clones) does not allow enough rearward tilting of the camera for motorcycle helmet chin mounting. I did find one here by another maker, https://www.thingiverse.com/thing:4228981 I knew I was probably going to have to make it a different offset for my helmet, so I just modeled my own version from scratch, in three different offsets. Each larger offset allows the camera to be tilted back farther.

These are designed to fit into the original GoPro (or clone) snap base with the three screws that come with the original J-Hook mount. These part files are for the J-Hook only and do not include the snap base assembly. The first file has an offset .5" (12.5mm) more than stock. The second file offset is plus .9" (23mm) and the third file is plus 1.25". (32mm)

Every helmet has a different shape and will usually require a custom mount. My helmet happens to be an HJC RPHA ST brand, which I have a custom mount for as well, if anyone needs one for that specific helmet. For my helmet, the extended j-hook 2 works perfectly with the camera tilted all the way rearward. This makes it easy to know it is in the correct position when it is pushed all the way back until it bottoms out on the mount. With three different sizes available, there should be a good fit for any helmet chin mount.

Update: I had a request for another J-hook with a larger rearward clearance than the previous largest one. I have uploaded a fourth GoPro_Extended_J_Hook_4.STL that has an additional 10mm (.40") rearward clearance.

Update 1: I included an original size J-Hook per request.