This is the case Mazda uses for organizing and storing rotor apex, side and corner seals. Rotors sides are numbered 1-6, which correspond with the numbers in the case. If you put the seals in the right place when taking things apart, it can make life much easier when reassembling. Also, you can fit seals, take them out and store them in the case, then just pop them back in the right spot when you do final assembly later, with no fear of mixing up the clearances. There is also room on top to put in the rest of the seals and oil control rings, so you can keep everything together. Limited quantity in stock. If sold out, it may take a couple weeks to special order more inventory from Mazda. Sorry for the price increase, Mazda has raised the price big time 10/13/2001.