These Planhold clamps are fully compatible with all other manufacturerâ€™s blueprint racks and stands. They are constructed extruded aluminum with polished chrome plated cast alloy wing knobs. Mounting clips are user friendly and will not stick or jam. Wing knobs are guaranteed for life. The entire clamp is warranted for 10 years. Holds 100 sheets or 20 pounds and come with green color label holders. They are packaged six per box.