Genuine GM Muffler Original For 1957 Pontiac Chieftain.  Genuine GM new old stock. Oldberg. GM part #524806 . For single exhaust. 2.25" ID inlet, 2" ID outlet. Body is 25" long x 8.25" wide x 4.25" thick. Some surface rust, but not bad. Perfect for your restoration project. Probably fits other years and models, but i can't say for sure wich ones.