1/4″ MFL to 1/4″ MPT Fitting
This fitting could be used for a lot of things. One potential use would be as part of a Spunding Valve Build. A Spunding Valve allows you to ferment under pressure, naturally and precisely carbonate in the keg, fix over-carbonated beers and more. This fitting would be part of a style 2 build.
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Make sure the components you use are compatible and rated for your intended application. Contact manufacturer with questions about suitability or a specific application. Always read and follow manufacturer directions.