This is 100% 304 stainless steel and will not rust. Eliminates the whistling and failures commonly occurring in single wall or mesh style flex pipes. Works well in high heat applications. Available in 42mm, 2", 2.5", or 3" diameters. 42mm is 4" long. 2" is 3" long. 2.5" couplers are 4" long. 42mm units work with 1 5/8" or 1 3/4" piping depending on whether you are welding into a slip fit or butt fit.