Sturdy 0.88' outer diameter 18-gauge steel tubing. Seat is a full 14' diameter with 11.5' diameter Masonite board that is recessed into the pan with eight rivets and will not chip or crack. Foot rings with 0.63' outer diameter are welded to each leg by four contact points for added rigidity. Backrest adjusts up/down and forward/back. Tested by Bureau Veritas to support 500 lbs static load capacity.