Cap for fuel or water or waste water tank on sailboats.
This is a model for a generic 40mm Fuel cap. Many (European) sailboats use this size of cap to seal the tanks for the fuel, water or waste water. The caps are all the same size and often only the colour is different. I had to design this one as the cap of my boat dropped in the water and the standard ones for sale did not fit. I printed it in ABS as it will be exposed to the sun 365 days per year.
It has 40mm rubber O-ring at the top. This size O-ring can be bought in many DIY shops. A quick search on Aliexpress for 40mm O-ring will give you many results as well. The design has an area just underneath the cap where the O-ring fits.