Perfect SCH 40 (1/8-3/16 thick tube) 1.6" ID // 1.9" OD TIG welded collectors 304 Stainless Tops come beveled for that perfect weld and penetration. Each collector is designed for the flange being used, you can tig weld the inside around the mating surface with ease... there is nothing better and this strong. Once you weld the inside as said the air flows with precision into the turbine!! No bs metal in the way just a straight clean shot, it doesnt get better. Welded inside and out