I've got to make me another, since years ago someone 'borrowed' mine.
If you can picture it...get a old deep 3/8" drive socket, one that will slip 'inside' the nipple. Also need a short piece of bar stock, the right thickness to fit the slots in the nipples. Then just a matter of putting a slot, or holes halfway up in the old socket, so the metal stock will stick out like tags. Simple deal to slide the socket into the nipple, engage the tangs, and turn. The socket fitting inside the nipple keeps it from changing shape, or damaging the nipple.
My original one was welded up, but don't have access to one now.
But, like said, depends on how tight the nipple is.