Injectors are sold as a set of 6 (Cummins) or a set of 8 (Duramax and Power Stroke). ALL CORES MUST BE SENT TO S&S. If you elect to ship your cores BEFORE receipt of the S&S injectors, your S&S injectors will not ship until S&S receives your cores. If you elect to ship your cores AFTER receipt of the S&S injectors, S&S must receive your cores within 30 days of purchase to receive your core charge refund. All S&S products have a 20% restocking fee. Injectors and CP3 pumps carry a 1 year unlimited mileage warranty. Contact S&S for any warranty concerns. Any suspect hardware must be returned to S&S for evaluation, and will be repaired or replaced at S&S discretion. Improper usage, damage, and fuel contamination are not covered.