Commercial & Residential Use, Multi-Size Door Closer. Adjustable Spring Power. Universal Application, Designed for Standard, Top Jamb, Parallel Arm Installtion. Closing and Latching Speed Controlled by Two Separate Regulating Valves. Standard Adjustable Back-Check & Delay Action Function. Precision Heavy Duty Rack (Pistion) & Pinion Gear. Factory Tested to Meet or Exceed ANSI standard 156.4 Optional FULL/SLIM Steel Cover or PVC cover