These have been an ongoing PITA for me on Mutt the Race Truck. The issue has been that I need a different flange to make up to my race-only thru-the-fender exhaust pipe and it's almost impossible to weld to those as they're as thin as tissue paper (well, not quite but you catch my drift). There's a guy in town who does welding for me when it's beyond my skill level and we has been able to make something work but 'tain't easy. I wish I could find a good aftermarket supplier so we could at lest start with a fresh one. TIG welding SS that is impregnated with crud isn't easy.