These are high-purity two-stage regulators for more accurate pressure regulation; highly recommended for GC applications. Gas contacts only brass, stainless steel, Kel-F® and Viton®, to assure purity. The first stage reduces tank pressure by about 90%. The second stage uses an extra-large 2-3/4" stainless steel diaphragm with the lower-pressure gas for sensitive control; the outlet pressure is held constant. A pressure-release valve after the first stage protects your instrument from over-pressurization; sintered-metal particle filters in the inlet keep out damaging metal filings. The body is made from chrome-plated brass. Maximum inlet pressure is 3000psig. The outlet is 1/4" female NPT. Attach 1/8" tubing with a male connector 1/4" NPT to 1/8" tube (not included).