You will find Stem bumpers typically on the bottom of round swivel base patio chairs. These stem bumpers act as glides to keep the round base of the outdoor chair from making direct contact with the ground. Swivel base outdoor chairs use between 6 and 8 stem bumpers per chair. Stem bumpers can be flat or coved (curved) to fit the shape of the tubular metal of the patio chair base. Round patio chair glides and stem bumpers are sized to fit common patio furniture chair.