All steel. Raw. Inside nub for 14"-16", 20" & 22" caps is 7 1/2". Inside nub for 17" & 18" caps is 7". C52 is only cap to fit 20". Image shown with custom yellow powder coat, trim ring & 1947-53 Chevy cap for Smoothie, not included. Lug nuts not included. Optional custom powder coat, $35/wheel. Please check fitment before mounting. Doesn't fit Jeep Samurai. Please note our 20" & 22" Smoothie centers DO NOT have the ring around the cap like our 15"-18" centers do. Please see our series 513 for picture of center detail.