Curtain tracks (Model 2800) shall be of 14 gauge galvanized steel construction, entirely enclosed except for slot in bottom, each half to be in one continuous piece except where splicing clamps are required. Each curtain carrier (Model 2801) shall be spaced on 12" centers and shall be of nylon (or steel) construction supported from a ball-bearing by two polyethylene wheels held to ball-bearing by rustproof nickel-plated rivet, such wheels rolling on two separate parallel treads. Each curtain carrier shall consist of a free-moving plated swivel and sufficient trim chain to accommodate curtain snap hook. Live-end pulley (Model 2803) and Dead-end pulley (Model 2804) blocks shall be adjustable and shall be equipped with 3" diameter sleeve-bearing wheels adequately guarded. A rubber bumper shall be attached to each curtain carrier to function as noise reducer. The manufacturer shall furnish two end stops (Model 2809) for placement at each track end and a tension floor pulley (Model 2865) for increasing cord tension. Stretch-resistant operating cord (Model 2828 for hand operation and Model 3529 for machine operation) shall have synthetic or wire center and shall be of 3/8", or 3/16" diameter. If Back-pack devices are used with this track Model 2833 is used for hand operated track systems and Model 2834 is used for machine operated track systems. Model 280 as manufactured by Automatic Devices Company of Allentown, PA.