People requested this after I made the C17 version and I finally got around to doing it. Works based on the same principle as the other one where the adapter is clamped between the lower rail and upper saddle material, in this case leather. I like how simple it is, I always hated those rail type light mounts/adapters.
Link to 3D print it yourself here. If you don't have a printer or want to support what I do you can buy it here with the screw and nut.
More detailed installation process in the links above but essentially you just push the leather away from the rail to get enough space to slide the thin part of the adapter in. Then pull it through as much as possible. Once it's in, it is very tight, I couldn't pull it out without purposely pushing the leather out of the way and since you'd be riding this and sitting on it, I doubt it will work it's way loose. I already sold my Be Seen lights so I don't have it to model here.
by edtse88