If you've ever tried to remove or install a nipple from a brass stove, you know how frustrating it can be. There is just so little room for a wrench to be able to move to loosen the nipple. I've obtained some Nipple Spanner tools from Butterfly. These are double jointed and fully articulating, so you can actually completely remove or install the nipple without removing and repositioning the tool. The tool works best when it is inserted just below the top of the burner (where the flame ring is). You then turn the nipple as far as it will go in one direction, then lower or raise the tool handle, turn the nipple further, then you twist the handle (right or left) and again turn the nipple. Repeat this process until the nipple is installed or removed.
A nipple is pictured with the tool, but is not included with the tool purchase. You can purchase the nipple on this website. This tool and four nipples are included in the 2412 Parts Kit.