Tranquiline Gas Flex Connectors come in various lengths to connect your gas supply (stub) to your Control Valve or Burner. These black, coated 3/8" connectors are suitable for Vent Free or other >40k Btu appliances. Some feature baffles to silence higher pressure applications on Natural Gas or Propane systems. They come with a 3/8 MIP(MPT) to 3/8 Flare, and a 1/2 FIP (FPT) to 3/8 Flare fitting, which will connect most up to code gas line installations to the respective control valve. (3/8 MIP(MPT) is by far the most commonly found gas input size on >40k btu appliances. **When choosing a flex, it's better to have extra length than be short. So, if you're debating length, opt for the longer of the two. The overall length includes the fittings, so a 24" flex only measures 22" without the fittings in place. The only brand that always comes with a flex connector is Real Fyre, for any other brand you'll need to purchase one.