Grundfos 529912 Pump 3/4" Bronze Half-Union Threaded End for Union Mounted Pumps-2PK

If you buy the Grundfos 10-16 union (which I would because it has the built-in check valve) you need to get the right union for your pipes. For me. that was the union to match up with 3/4 inch Bronze MPT. This installed very easily. I just tightened about a quarter turn more than hand tight and there's no leaks.