Ordered a new spray arm (because the old one finally broke into two pieces after falling off several times, and this time the arm melted next to the heat coils) AND ordered the new nut because of all the information posted by other users (thank you). Had to use pliers to get the old nut to unscrew, but once it was off, getting the new nut in was easy. Then popped on the new spray arm, and voila, the next load of dishes came out much cleaner! Yay!