This is a floating handle for GoPro cameras. It's only 115mm tall so it will fit on almost any printer. I have only tested it with the Hero 5, but I'm pretty sure it will float with any other GoPro camera. For reference, the Hero 5 with the frame and a battery installed weighs ~170g.
You'll need an M5 nut for the screw and a bit string or rope <4mm in diameter for a lanyard if you want (I used paracord and it works pretty well).
Use a lot of top layers to make the mounting part solid (88 top layers for 0.2mm layer height). Alternatively, you can use the variable settings wizard in Simplify3D to print at 100% infill for everything above 98mm, and 15% infill for everything below. This will make the mount much stronger while still maintaining buoyancy.