WHISTLE FREE - Multi-pattern corrugation disrupts the vibrations that cause whistling. INDOOR / OUTDOOR - Great for gas fire pits, gas log sets, fireplaces, and other fire features. SPECIFICATIONS- 1/2-inch MIP to 1/2-inch FIP fittings and 1/2-Inch ID x 5/8-Inch OD STAINLESS STEEL - Stainless steel construction for durability and longevity. NG/LP - Works with natural gas and propane appliances. Midwest Hearth Whistle Free gas lines are perfect for fire pits, gas log sets, fireplaces and more. Stainless steel construction with brass fittings.