BOSS Office Products BLACK HIGH BACK TASK CHAIR, BL-0021 High-back styling upholstered with commercial grade fabric. Sculptured waterfall seat made from molded foam that contours to the shape of your body. Ratchet back height adjustment allows perfect positioning of the back cushion for lumbar support. Adjustable height armrests with soft polyurethane. Width adjustable armrest allows the user to move the armrests to match shoulder breadth. Large 27" nylon base for greater stability. Hooded double wheel casters. Pneumatic gas lift seat height adjustment. Adjustable tilt tension control. Seat tilt lock allows the seat to lock throughout the tilt range. Back angle lock allows the back to lock throughout the angle range for perfect back support.