This replacement stainless steel lid works with Marchisio style variable capacity tanks measuring 500mm in diameter. The size refers to the diameter of the tank they fit in, not the actual diameter of the lid. These should work non-Marchisio style tanks as long as the diameter matches up.
These lids are designed to work with the following standard style Marchisio Variable capacity tanks. For non-Marchisio style tanks, as long as the diameter of your tank is 500mm, these should work.