The Cummins Diesel Oxidation Catalyst (OEM Number 3999660) is a highly practical and efficient solution for Cummins models. Made with a silicon carbide substrate material and a stainless steel canister, this catalyst ensures optimal performance. Each purchase includes 1 Diesel Oxidation Catalyst, 2 gaskets, and 2 clamps. Please note that this product is not CARB compliant and cannot be sold in California. With its compatibility with various OEM and aftermarket numbers (3999660, 3103618, Q619723, and Q619494), this catalyst is a reliable choice for diesel engines.