These 45000 Long-Tube GM LS Engine Swap Headers fit 1994-2003 Chevy and GMC 2WD (only) S-10, S-15 trucks and 1982-2004 Blazer and Jimmy. They have a mild steel construction, and use smooth flowing, 1-3/4 in. diameter, CNC mandrel bent tubes designed to run inside the frame. The stout 3/8 in. header flanges ensure a great seal that will resist warping, and the high-flow 3 in. race collectors ensure unimpeded exhaust flow for maximum performance.