This zinc is used in your Universal diesel engine's heat exchanger. Its purpose is to reduce corrosion inside. Just like the zinc on your prop shaft or strut, it needs to be replaced periodically, at least once per year. Replace it even if it is still intact. The least noble portion of the zinc may have already done its job and no longer be available to prevent corrosion even though it still looks OK.
This part number has a 1/8" pipe thread. As this is difficult to measure, determine the correct size by fitting a wrench to the hex head. If you need a 7/16" wrench for the drain plug on your heat exchanger, this is the correct zinc.
1) Unfortunately, it is not possible to determine which zinc you need based on engine model. The only way to know which zinc you need is to determine which wrench size fits the drain plug.
2) Be careful not to drop the zinc. It will break where the rod is screwed into the brass plug.