All steel, matte black & chrome. Inside nubs for 17" & 18" caps is 7". Inside nubs for 20" cap is 7 1/2". C52 cap included with all wheel sizes and is the only cap that fits 20". Lug nuts not included. Dual bolt pattern wheels have 10 bolt holes. Please note that 17" & 18" options have a ring around the hubcap area, the 20" & 22" options do not (see photos). See Series 513 for center detail photos. A reverse rim is used for 517-8010400 to achieve backspace. Doesn't fit Jeep Samurai.