This is a float switch mounting bracket that clips onto the output pipe of a ReefOctopus Essense S-130 Skimmer. When printed in PETG (which is aquarium safe) and at 25% infill, the clip bends open enough to slip right onto the output pipe and friction keeps the mount in place. It can be slid up or down the pipe to get the float switch height just right for your particular water level and switch. The pipe clip is 1cm tall. The switch mount portion is 3mm thick and has a 13mm diameter opening which should fit most 1/2" float switches. The S-130 specs show a 40mm output pipe but did not specify if that was ID or OD. To be safe, I printed brackets for a 42mm, 40mm, and 38mm pipe; the 38mm fit the best with enough friction to stay in place.

For a little background (especially if you aren't into aquariums), a protein skimmer removes dissolved organics in the water. Most protein skimmers are designed to work with a certain water depth. When you shut off some pumps (for feeding or maintenance), the water in the protein skimmer can rise causing it to overflow. A float switch can be connected to an aquarium automation controller (aka Neptune Apex via a Break-Out-Box module) which will shut off the skimmer if the float switch is triggered.