Heavy WT Shock Proof Gear Lube Firm thickness greater than SAW 75W250, yet low fluid friction like 75W90. For heavily-loaded racing differentials and transmissions, problem gearboxes. Most popular ShockProof product, many racing and specialty applications. Often used in Sprint Car, Midget, and Dirt Late Model Differentials. Most popular gear oil in NHRA Top Fuel and Funny Car.