Ball-lock gas disconnect (MFL, check valve): snaps over the gas post; 1/4" MFL (7/16-20 UNF) tail, often with an integrated check valve, snap-on gas quick disconnect, seals on O-ring over the post shoulder; flare face at the MFL tail. What it fits and the adapters to join it to other keg fittings.
Updated 05 September 2026.
Ball-lock gas disconnect (MFL, check valve) (grey QD, 1/4" MFL tail)
Where grey QD, 1/4" MFL tail is used, its real dimensions, and how to connect it to other keg fittings.
Published dimensions
- Designation
- grey QD, 1/4" MFL tail
- Size / thread
- snaps over the gas post; 1/4" MFL (7/16-20 UNF) tail, often with an integrated check valve
- Fitting form
- snap-on gas quick disconnect
- Seals on
- O-ring over the post shoulder; flare face at the MFL tail
- Rating / role
- the gas-side ball-lock disconnect, keyed to the gas post and usually grey or white
Used on: the CO2 side of a ball-lock corny keg, taking an FFL swivel or a push-in flare fitting on the MFL tail.
The gas ball-lock disconnect is keyed so it only fits the gas post, and many carry an integrated check valve so a foamed keg cannot push beer back up the gas line. Its 1/4 MFL tail seals on the flare, so pair it with an FFL swivel or push-in flare fitting, not tape.
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 Ball-lock gas disconnect (MFL, check valve) (grey QD, 1/4" MFL tail)?
grey QD, 1/4" MFL tail
What is the size / thread of the Ball-lock gas disconnect (MFL, check valve) (grey QD, 1/4" MFL tail)?
snaps over the gas post; 1/4" MFL (7/16-20 UNF) tail, often with an integrated check valve
What is the fitting form of the Ball-lock gas disconnect (MFL, check valve) (grey QD, 1/4" MFL tail)?
snap-on gas quick disconnect
What is the seals on of the Ball-lock gas disconnect (MFL, check valve) (grey QD, 1/4" MFL tail)?
O-ring over the post shoulder; flare face at the MFL tail