This muffler is polished stainless steel. The part number is 4040XL. It has 4 inch inlet and 4 inch outlet. It was on my truck for a month. I found it was too loud for me while towing my 10k travel trailer. I perfer to hear my turbo sing than the exhaust. It was never welded, but rather used band clamps. Purchased from Parleys Diesel. Asking $100. PM me for pics and additional information.