What Adapter For
Your answer

What size is my shut off valve?

A shutoff valve’s outlet, where the supply line connects, is almost always 3/8" compression on a sink or toilet valve. Its inlet matches the pipe in the wall: for 1/2" copper or PEX, it’s 1/2" nominal, which is 5/8" across.

What comes out of the wall?

A small valve with a handleA shutoff valve. Its outlet is usually 3/8" compressionBare metal pipe, no valveCopper, 5/8" acrossBare plastic tubing, no valvePEX, 5/8" across

You most likely have

Shutoff valve under a sink or toilet

The small valve on the wall. Its outlet is usually 3/8" compression.

On the package: 3/8 in. compression outlet

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3/8" compression supply lines
  • A faucet or toilet supply line with a 3/8" compression nut threads onto it.
  • Tighten it the way the line’s instructions say, with no tape or sealant. BrassCraft lines go hand-tight plus a quarter turn, and Fluidmaster toilet lines half a turn past hand-tight.

Connect it to

Faucet with threaded tailpiecesFaucet with its own hosesToilet tankDishwasherRefrigerator ice maker
Start over

You most likely have

1/2" copper pipe out of the wall

No valve yet. 5/8" across.

On the package: 1/2 in. nominal copper, 5/8 in. O.D.

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1/2" nominal x 3/8" compression angle stop
  • A 1/2" nominal compression x 3/8" compression angle stop goes on it without soldering.
  • Turn the water off first, and check that the pipe end is round, square and free of burrs.

Connect it to

A new shutoff valve
Start over

You most likely have

1/2" PEX tubing out of the wall

No valve yet. Plastic, 5/8" across.

On the package: 1/2 in. PEX

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1/2" PEX x 3/8" compression angle stop
  • Shutoff valves come with crimp, expansion or push-connect inlets for PEX. Match the one your PEX joints use.
  • Shut the water off before you fit the valve.

Connect it to

A new shutoff valve
Start over

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Outlet sizes

3/8" O.D. compression takes a 3/8" tube, the size standard faucet and toilet supply lines have. BrassCraft also makes valves with 1/2", 7/16" and 1/4" O.D. outlets; the 1/4" one is for ice makers. A supply line nut that won’t start by hand is usually the wrong size, so check before using a wrench.

Inlet types

Picking the supply line next?

Faucet supply line size

Common questions

What size is a toilet shut off valve?

The same as a sink valve: a 3/8" compression outlet in most homes. The toilet's supply line runs from that outlet to the 7/8" thread on the tank's fill valve.

What does 1/2 inch nominal mean on a valve?

It means the valve is for 1/2" pipe, which is 5/8" across for copper and PEX. A valve marked 1/2" O.D. is a different, smaller size and won't fit that pipe.

Keep going

Identify itany partShutoff valve for copper pipeShutoff valve for PEXFaucet supply line sizeToilet supply line size

Where we get our information from

The sizes on this page come from published standards and the makers’ own documents. Checked against published data from BrassCraft, Copper Development Association, Uponor and Fluidmaster.

See all 6 sources
  • Copper Development Association, Copper Tube Handbook (ASTM B88 tube dimensions)
  • Uponor, Plumbing Design Assistance Manual (PEX is copper tube size)
  • BrassCraft, angle stop product pages (compression, FIP, sweat, PEX and push-connect inlets; 3/8", 7/16", 1/2" and 1/4" O.D. outlets; 1/2" nominal = 5/8" O.D.)
  • BrassCraft, toilet connector 3/8" comp x 7/8" ballcock and submittal 400.339
  • Fluidmaster, faucet and toilet connector catalogs and Click Seal pages (FM91429, FM91233)
  • BrassCraft, installation instructions for connectors (425.10, 425.07, B0120IMB) and water supply stops (425.04)

General guidance from manufacturer and standards data. Parts vary by brand, so check the size printed on the package against what you measured. For gas lines or anything inside a wall, use a licensed plumber.