These 304 Stainless Steel pipes are perfect for exhaust manifold/header fabrication. They have a uniform inner diameter and high quality finish that will look great when installed. Sometimes called "weld el's", they are designed to be welded to each other and will work perfectly with our other exhaust fabrication parts. ** Please note that NPS stands for Nominal Pipe Standard. This means that the size denoted in the title does not refer to an exact inner diameter. Please refer to an NPS chart to determine actual sizing. **