The APR Race Midpipes are both 2.5" and are designed as a simple plug and play upgrade. We use T304 stainless steel piping that's brushed, mandrel bent, and TIG welded to the included CNC machined ultra-flat OEM-style 3-bolt-flanges. The system includes new gaskets, bolts and copper plated nuts., , The APR Race Midpipes are compatible with the factory DP and our Race DP. Race Midpipes (catted or non-catted) are required for Stage 2 along with our Race DP.