Most sink supply lines are 3/8" compression x 1/2" FIP: the small end goes on the shutoff valve, the big end on the faucet. A toilet needs 3/8" compression x 7/8" ballcock.
I have
Shutoff valve under a sink or toilet
The small valve on the wall. Its outlet is usually 3/8" compression
Threaded 1/2" shanks under the sink, no hoses attached
What fits
3/8" compression x 1/2" FIP faucet supply line
On the package: 3/8 in. Comp x 1/2 in. FIP
one per tap, so two for a hot and cold faucet
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If your faucet already has hoses hanging from it, you don’t need supply lines at all.
Which line fits
A supply line is named by its two ends, valve end first. 3/8" compression is the size of the shutoff valve’s outlet. 1/2" FIP (female pipe thread) is a nut with threads inside that screws onto the faucet’s threaded shank.
Check the valve outlet first
The shutoff valve’s outlet is usually 3/8" O.D. compression, meaning it takes a 3/8" tube. BrassCraft also makes valves with 1/2", 7/16" and 1/4" O.D. outlets (1/4" is the ice maker size), and supply lines come in matching versions. If the line’s nut won’t start on the valve by hand, stop and check the size rather than forcing it. To check, measure it.
The faucet end: shank or hoses?
- Threaded shanks, no hoses: the faucet has threaded 1/2" shanks (Moen calls them 1/2" IPS; Delta lists the thread as 1/2"-14 NPSM, a straight pipe thread). Use a line with a 1/2" FIP nut, one for each tap.
- Hoses already attached: Moen and Kohler faucets of this type come with flexible lines ending in 3/8" compression nuts. They go straight onto the valves.
How long?
Measure from the valve outlet to where the line connects, following a gentle curve rather than a straight line, then choose the next length up. A line a few inches too long can loop. A short one can’t be stretched. Don’t let the line be pinched or trapped, and protect it from sharp edges such as a hole in the cabinet side.
Installing it
- Start with the shutoff valve closed. Afterwards, open it slowly and check each end for leaks.
- No tape or pipe dope. Braided lines seal with washers built into the nuts. Don’t use thread sealant on them.
- Tighten to the package instructions, which differ by brand. BrassCraft lines go hand-tight at the faucet and hand-tight plus 1/4 turn at the valve. Fluidmaster toilet lines go 1/2 turn past hand-tight at the valve. Click-seal nuts go hand-tight until they click.
- Replace old lines. Swap out any supply connector that is worn or over 5 years old.
No shutoff valve yet?
If a bare pipe comes out of the wall, shut off the water to it first (usually the house’s main shutoff). The valve’s inlet has to match the pipe. For 1/2" copper, use a 1/2" nominal compression inlet (1/2" nominal is 5/8" O.D.), a sweat inlet, or a push-connect inlet; for PEX, a crimp, expansion or push-connect inlet. The outlet is 3/8" compression either way. The adapter finder walks through each.