Reliance 546 Hydraulic Stool with Adjustable Backrest Model 546 enhances the versatile design of the Model 540 by adding an adjustable, tilting, upholstered backrest Features Five-legged, 19.75″ diameter base Hydraulic raising and lowering with foot pedal provides hands-free height adjustment 15″ round seat and tilting adjustable back An optional specially designed floor lock to prevent chair movement during surgical procedures Seat rotation locks by lifting foot pedal Standard height elevates from 17″ to 25″ above the floor. Medium seat height for surgical use is 20½” to 28″. High seat height is 24″ to 31½” Available in a variety of upholstery colors Made in U.S.A.