Hard to find Flex Hose at the right sizes as you probably already know, which is why we have this Flex Hose special made. 

10 FT of 1 7/8 inch Stainless Interlocking Flex Hose fits perfectly on a 1 1/2 inch Pipe nipple giving an Air Tight Connection for all your Truck Mount Engine Header & Heat Exchanger Exhaust Connections.

https://www.truckmountstore.com/1-1-2-inch-all-stainless-mighty-might-exhaust-diverter/