Inline gas check valve: 1/4" FFL (7/16-20 UNF) inlet and 1/4" MFL (7/16-20 UNF) outlet, or barb ends, one-way flare check valve, seals on flare faces at each flare end; barb under a clamp on barb versions. What it fits and the adapters to join it to other keg fittings.
Updated 05 September 2026.
Inline gas check valve (1/4" FFL x 1/4" MFL)
Where 1/4" FFL x 1/4" MFL is used, its real dimensions, and how to connect it to other keg fittings.
Published dimensions
- Designation
- 1/4" FFL x 1/4" MFL
- Size / thread
- 1/4" FFL (7/16-20 UNF) inlet and 1/4" MFL (7/16-20 UNF) outlet, or barb ends
- Fitting form
- one-way flare check valve
- Seals on
- flare faces at each flare end; barb under a clamp on barb versions
- Rating / role
- passes CO2 toward the keg and blocks beer or foam from returning up the gas line
Used on: between a regulator or manifold and the keg gas post, on the gas line only.
A gas check valve is directional, so it must face the keg or it will block the CO2 you are trying to add. The common homebrew version has a 1/4 FFL inlet and 1/4 MFL outlet, seals on its flare faces and needs no tape. Fit it on the gas line, never the beer line, where it would stop the pour.
Flare fittings seal on the 45 degree flare face and must never be taped. Push-in fittings seal on an O-ring against the tube wall and need the tube cut square. Barbs seal under a worm clamp. Getting the sealing method right matters more than the thread label, because most homebrew leaks are a taped flare or an unclamped barb.
Connect this fitting
Questions and answers
What is the designation of the Inline gas check valve (1/4" FFL x 1/4" MFL)?
1/4" FFL x 1/4" MFL
What is the size / thread of the Inline gas check valve (1/4" FFL x 1/4" MFL)?
1/4" FFL (7/16-20 UNF) inlet and 1/4" MFL (7/16-20 UNF) outlet, or barb ends
What is the fitting form of the Inline gas check valve (1/4" FFL x 1/4" MFL)?
one-way flare check valve
What is the seals on of the Inline gas check valve (1/4" FFL x 1/4" MFL)?
flare faces at each flare end; barb under a clamp on barb versions