Single Stage Side Entry Oxygen. This Gas Arc Single-Stage Regulator is CE Approved and Marked and manufactured under strict BS EN ISO 13485 quality design and management systems at Gas Arc''s UK production facility. Designed for use with Oxygen cylinders. Side entry pin index connection with O Ring seat and handwheel for easy connection. Robust brass body construction for prolonged service life. Serial number and replacement date clearly marked on rear of regulator.