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- 3/4-inch MIP to 3/4-inch FIP fittings and 3/4-Inch ID STAINLESS STEEL - Stainless steel construction for durability and longevity. NG/LP - Works with natural gas and propane appliances. Features: - Tranquil whistle free design helps to eliminate whistling noises. - Indoor or outdoor. - 3/4-inch MIP to 3/4-inch FIP fittings and 3/4-Inch ID. - Stainless steel construction. Compatibility: ✔ Gas Fire Pits ✔ Gas Fireplaces ✔ Gas Log Sets ✔ Natural Gas ✔ Propane How to reduce or eliminate whistling: - Use a whistle-free gas flex line. - Make sure there are no major bends or kinks in the line (90-degree bends will cause whistling). - Use correct gas pressure. Too high pressure can result in whistling even with the correct line.