This is a tuned pipe that fits a .19-.35 sized engine. A tuned pipe will quiet/muffle an engine and INCREASE the power and RPM of the engine. It is made of aircraft grade aluminum. This pipe REQUIRES an exhaust adaptor (header) to fit the engine (Macs makes a bunch) and a piece of silicone tubing (also called a tuned pipe coupler). Outer Diameter: 5/8" (16mm) Updated 7/15/92 JBN *8) BOX DIMENSIONS: 3.63" W. X 1.38" H. X 13.63" L. BOX WEIGHT: .12 LBS. Macs ProductsPart MAC1120