These flanges are sold as a set (2) 3/8" thick steel header flanges are manufactured to be used with 1-1/2" OD exhaust tubing. We also offer these flanges for 1-5/8" exhaust tubing. These header flanges are made of 3/8" thick cold rolled steel and are CNC machined for a precise fit to you engine heads.The added length on the right hand flange is provided for the mounting of the EGR tubing, if required. When ordering, please specify if EGR is required. If EGR is not required, we trim off the excess flange length.