You might want to give Spartan a call. Have your serial number handy when you call as they can then look up your specific chassis and know exactly the air bag that is on it. Sometimes they have the best prices on "stuff" for your chassis. I have ordered filters and other items directly from them as they had the best price that I could find.
Dave and Karen -- '02 Ultimate Advantage 36 C, 350 HP Cummins, Allison 3060 Tranny
'07 Ford Escort, Brake Master 4160, '13 Ford Edge, InvisiBrake