Firestone Sport-Rite Air Helper Spring W21-760-9000. Tapered Sleeve 9000 air bag with 1/4 NPT Air Inlet. BCR: 9.9 inches, Cap Number: 6988, NBD-15305, Compressed Height: : 4.30, Extended Height: 11.50, Extended Length (IN): 10.25 inches, Firestone Part Number: W21-760-9000, Maximum Diameter: 5.7 inches, Piston Number: 7572, NBD-14048, Ride Height: 8.25 inches.,