Dreffco 1/2" x 18" Black Non-Whistle Flexible Flex Gas Line for NG or LP For Use Indoors or Out 1/2" Female Flared Fitting Each End. We've Included 1/2" Male and Female NPT Fittings For Your Convenience 18" 1/2" Non-Whisle Flex line is 1/2" OD and 3/8" ID x 16-3/4" Long w/o Fittings There Is a Staggered Pitch Every 2" to Eliminate Whistling Typicall Use Is for NG or LP Fire Features &gt;100K BTU with a 1/2" Connection Hub