The Mack Replacement Pipe is a practical solution for replacing the 4ME-21781 OEM part in most RM Mack makes and models. With a 4" diameter and aluminized construction, this pipe offers durability and a perfect fit. Sold individually, it is a cost-effective option for maintaining your Mack truck's exhaust system. Upgrade your vehicle with this reliable replacement pipe that ensures optimal performance and longevity.