The Aero Exhaust tip are made out of T304 stainless steel that is polished to a mirror finish and then embossed with the Aero Exhaust logo. They have a dual wall that allows air to flow around. This feature keeps the tips cool and helps them to avoid discoloring. The ST3040 is a 3" ID with a 4" OD and are approximately 10 inches long. These tips are great on Dodge Hemi trucks and cars with upgraded tail pipes such as the Chevrolet Camaro and Dodge Challanger.