I have a float i bought in China but it's diameter is a bit to big for my kids (age 3 & 6) to hold properly.

Designed this one with a smaller diameter of 30 mm for better grip for the kids.

Made the walls thin to get as much air inside as possible, and added a disc in the middle of the handle to stiffen it up.

The float has positive Buoyancy on my GoPro 3+ hero in its watertight housing, but not enough Buoyancy to float my Gopro Hero 5 black.

They weigh of both camera's is almost the same, but the added air inside the Gopro 3+ housing makes the difference i think.

I made 2 versions.

One with only the float and one where i added a thin base to stabilize while printing. I had a problem with the float breaking away from the printing bed, when it got near to completion because of vibrations from the printerhead so i added the base.

The base easily cuts away after printing.

The hexagonal hole for the nut is made a bit tight so the bolt needs to be pushed in with a bit of force, this has the advantage that the nut does not have to be glued into the hole.