Steel. Complete kit in black wrinkle finish with everything you need. Includes 2 flanges (84-03 style/17-22 style) and 2 retainers. OEM replacement reference 65328-83; 65328-83A steel flange and 65325-83A retaining rings. Note: 84-03/17-up ”Early Style” steel and 04-17 ”Late Style” plain aluminum exhaust flanges are interchangeable. Late Style flanges are thicker and designed to help prevent bending of the exhaust flange. All will fit all 84-up Big Twin and 86-up XL Sportster models. M8 models are equipped with the ”early style” steel flanges again.