What Supply Line Size Does an Allen + Roth Faucet Need — and How Do You Get It Right?

If you’re staring at a new faucet box and wondering about the allen roth faucet supply line size, you’re not overthinking it — supply lines are the one connection that quietly causes half the leaks and returns in DIY faucet installs. Get the size and the connection type right and the whole job takes fifteen minutes. Get it wrong and you’re back at the hardware store with a wet cabinet floor. Below is exactly what size you need, why the numbers can look confusing, and how to connect it so it never drips.

What Size Supply Line Does an Allen + Roth Faucet Actually Use?

For the vast majority of Allen + Roth faucets, the answer is a 3/8-inch compression connection at the valve end and either a 3/8″ or 1/2″ connection at the faucet end. Allen + Roth is Lowe’s house brand, and like most US-market faucets it’s built to standard North American plumbing sizes — there’s nothing proprietary about the threads.

Here’s where people get tripped up: the “3/8-inch” doesn’t refer to a diameter you can measure with a ruler across the fitting. It’s a nominal compression size that matches your under-sink shutoff (angle stop) valve. That’s why you’ll see a supply line labeled 3/8″ comp x 1/2″ FIP — one end fits the 3/8″ compression stop, the other threads onto the faucet’s 1/2″ male tailpiece.

Break it down by faucet type and it gets simple:

• Allen + Roth kitchen faucets (pull-down/pull-out): The hot and cold supply hoses are usually pre-attached to the faucet body. They terminate in 3/8″ compression female nuts that thread directly onto your 3/8″ shutoff valve. You often don’t buy separate supply lines at all.
• Allen + Roth bathroom faucets (centerset, widespread, single-hole): These typically have 1/2″ female threaded inlet shanks under the sink. You supply your own braided lines, sized 3/8″ compression x 1/2″ FIP.
• The shutoff valve end (both cases): Almost always 3/8″ compression. This is the US standard for angle stops under a sink.

Why Do Supply Lines Have Two Different Numbers Like “3/8 x 1/2”?

Because each end of the line connects to something different, and those two somethings almost never share the same size. The first number is the valve-side connection; the second is the faucet-side connection. On a typical Allen + Roth bathroom install, you want 3/8″ compression (valve) x 1/2″ FIP (faucet).

Let’s decode the abbreviations, because the packaging assumes you already speak plumbing:

• COMP (compression): Slips over the smooth outside of the shutoff valve stub and seals with a brass ferrule and nut. No threads to match on the tube itself — the nut does the sealing.
• FIP / FPT (female iron/pipe thread): A threaded female nut that screws onto the male threaded tailpiece under your faucet. “1/2″ FIP” is the standard faucet inlet.
• MIP (male iron pipe): The male version, less common on faucet supply lines but shows up on some adapters.

So “3/8 comp x 1/2 FIP” literally reads: 3/8-inch compression on one end, 1/2-inch female threaded on the other. That single line covers roughly 90% of Allen + Roth bathroom faucet installs in the US. If your faucet came with the hoses already attached (common on kitchen models), you skip the FIP end entirely and just need the 3/8″ compression nut to reach your stop valve.

How Do I Know If My Faucet Needs 3/8″ or 1/2″ at the Faucet End?

Look at what’s hanging down from the faucet under the sink — that tells you everything in about ten seconds. If you see rigid or flexible hoses already attached ending in nuts, measure across the nut opening or read the label; those are almost always 3/8″ compression female. If you see bare threaded metal or plastic shanks sticking down with no hose, that’s a 1/2″ male threaded inlet waiting for your supply line.

A quick field trick: a 3/8″ compression female nut is noticeably smaller — roughly 5/8″ across the flats — while a 1/2″ FIP connection is chunkier, around 3/4″. If you can thread a standard garden-variety 1/2″ supply line nut onto the faucet shank by hand, you’ve confirmed 1/2″ FIP.

One more thing worth checking before you buy: length. Supply lines come in 12″, 16″, 20″, and 30″ braided versions. Measure from the top of your shutoff valve to the faucet inlet and add a few inches of slack so the line curves gently instead of kinking. A kinked supply line restricts flow — and if you’re already fighting weak flow on one side, that matters. If your cold side runs weak after install, the supply line or valve is a prime suspect, and this walkthrough on why only the cold side runs at low pressure covers the exact diagnostic steps.

What’s the Difference Between Braided Steel and Poly Supply Lines?

For an Allen + Roth faucet, buy braided stainless steel supply lines — they’re the safest, most reliable choice and cost only a dollar or two more than plastic. Braided lines resist bursting, handle heat, and flex without kinking, which is why most plumbers won’t install anything else.

Here’s how the common options stack up:

Unless you have an exposed pedestal-sink situation where a shiny chrome riser looks intentional, braided stainless is the move. It’s forgiving of small alignment imperfections, which is exactly what you want when you’re working blind in the back of a cabinet.

How Do You Connect the Supply Line Without It Leaking?

The single biggest secret to a leak-free supply line is this: hand-tighten, then add only a quarter to half turn with a wrench — no more. These connections seal on a rubber or nylon washer (at the FIP end) and a brass ferrule (at the compression end), not on brute force. Over-tightening crushes the washer, distorts the ferrule, and actually causes the leak you’re trying to prevent.

Here’s the clean sequence:

1. Shut off the water. Turn both angle stops clockwise until they stop, then open the faucet to relieve pressure.
2. Attach the faucet end first (the 1/2″ FIP nut). Thread it onto the faucet’s male shank by hand until snug. The built-in washer does the sealing — no tape needed on FIP connections.
3. Attach the valve end (the 3/8″ compression nut). Thread it onto the shutoff by hand, keeping the line straight so you don’t cross-thread.
4. Snug both with a wrench. A quarter to half turn past hand-tight. Hold the valve body with a second wrench so you don’t twist the stop and crack a solder joint behind the wall.
5. Turn the water back on slowly and watch each connection for 60 seconds. A bead of water means back off, reseat, and try again — don’t just crank harder.

When do you need thread seal tape? Only on tapered pipe threads (MIP/NPT), like if you’re adding an adapter. You do not tape compression connections or FIP-to-faucet connections that seal on a washer. Adding tape there can actually keep the washer from seating and create a slow drip.

If you’re replacing an old faucet, this is also the perfect moment to swap in fresh supply lines and, if the shutoff feels stiff or weeps, new angle stops too. Old rubber-washer stops fail right when you finally close them. And while you’re under there, if the faucet itself has been dripping, the fix may be upstream of the supply line entirely — our guide on the cartridge inside a faucet handle explains why a drip usually points to the cartridge, not the supply connection.

Do Kitchen and Bathroom Allen + Roth Faucets Use the Same Supply Line?

No — and this is the most common mismatch. Kitchen Allen + Roth faucets usually arrive with supply hoses pre-attached ending in 3/8″ compression, while bathroom models expect you to buy 3/8″ x 1/2″ FIP lines separately. Same 3/8″ compression at the wall; different faucet-end story.

Kitchen pull-downs also carry a third hose — the quick-connect line for the spray head — which is internal to the faucet and has nothing to do with your wall supply. Don’t confuse that hose for a supply line; it stays coiled inside the cabinet and clicks into the pull-down wand.

If you’re planning a bathroom faucet purchase and haven’t picked the configuration yet, the number of supply connections depends on whether you go centerset, widespread, or single-hole — a widespread faucet has two separate valve bodies, each needing its own supply line. Our breakdown of centerset vs. widespread vs. single-hole bathroom faucets lays out exactly how many lines each style needs so you buy the right count the first time.

What If My Shutoff Valve Isn’t 3/8″ Compression?

Then you adapt — you don’t force it. Most US homes have 3/8″ compression angle stops, but you may run into 1/2″ compression, 1/2″ MIP/sweat, or 7/16″ & 1/2″ “universal” dual-outlet stops, especially in older houses or new builds with PEX. The fix is a cheap adapter or a supply line sized to match the valve you actually have.

Quick reality check on common scenarios:

• Valve is 1/2″ compression: Buy a 1/2″ comp x 1/2″ FIP line instead of 3/8″.
• Valve is 3/8″ comp (standard): Use the 3/8″ comp x 1/2″ FIP line — the default.
• You added a water filter or RO unit under the sink: These often tee into the cold supply and can change your hole and fitting needs. If you’re drilling for a dedicated dispenser, our guide on the correct RO water faucet hole size covers the sizing so you don’t over-drill.
• You’re not sure what you have: Take a phone photo of the valve and the faucet inlet to the store. Any plumbing associate can match it in thirty seconds.

One caution: never mix a compression nut with a threaded stub or vice versa. If the nut spins freely and won’t bite, or bottoms out after one turn, you’ve got a mismatch — stop and get the right adapter rather than forcing it, which strips the threads and guarantees a leak.

How Long Do Supply Lines Last, and When Should You Replace Them?

Braided stainless supply lines typically last 8–10 years, but you should replace them anytime you pull a faucet, and inspect them yearly. A supply line that fails while you’re on vacation is one of the top causes of catastrophic home water damage — the small cost of a fresh $6 line is cheap insurance.

Replace immediately if you see any of these:

• Rust bleeding through the braid or a bulge in the hose
• Green/white corrosion crust on the nuts
• Any dampness or drip at a connection that persists after a proper re-seat
• A stiff, kinked, or over-bent line restricting flow

If flow at the faucet is weak but the supply lines look fine, the culprit is often downstream — a clogged aerator is the number-one cause of a sudden trickle, and clearing it takes two minutes. Our walkthrough on a blocked faucet aerator shows how to rule that out before you blame the plumbing.

FAQ

Are all Allen + Roth faucet supply lines 3/8 inch?

At the shutoff-valve end, yes — nearly all Allen + Roth faucets connect to a standard 3/8″ compression angle stop. The faucet end differs: kitchen models usually have pre-attached hoses ending in 3/8″ compression, while bathroom models use a 1/2″ FIP inlet that pairs with a 3/8″ comp x 1/2″ FIP supply line.

Do I need to use plumber’s tape on the supply line connection?

No, not on the standard connections. Both the compression end (valve side) and the FIP end (faucet side) seal on a ferrule or a built-in washer, so tape isn’t needed and can actually cause a slow leak. Only use thread seal tape on tapered pipe threads (NPT/MIP), such as an adapter fitting.

What length supply line should I buy for an Allen + Roth faucet?

Measure from the top of your shutoff valve to the faucet inlet, then add 3–4 inches of slack so the line curves gently without kinking. Most bathroom installs use 12″ or 16″ lines; deeper cabinets or floor-level valves may need 20″ or 30″.

Why is my Allen + Roth faucet leaking at the supply line after install?

The two usual causes are over-tightening (which crushes the washer or ferrule) and cross-threading. Shut off the water, disconnect, inspect the washer and ferrule for damage, reseat the line straight, then hand-tighten plus only a quarter to half turn with a wrench. If the leak persists, replace the line — a $6 fix.

Can I reuse my old supply lines with a new Allen + Roth faucet?

You can if they’re braided stainless, under about 5 years old, and show no corrosion or bulging — but replacing them is smart. New lines cost a few dollars, seal reliably against the new faucet’s washers, and remove the biggest variable in a leak-free install. Never reuse old vinyl/poly lines.

What size wrench do I need to connect the supply lines?

An adjustable wrench handles every connection here. The 3/8″ compression nuts and 1/2″ FIP nuts fall in the 5/8″–3/4″ range, so one adjustable (or a basic pair) covers both ends. Keep a second wrench on hand to hold the shutoff valve steady while you tighten.

Author note: This guide was written by the evefaucet fixtures team, who install and bench-test kitchen and bath faucets across every major finish and connection standard. evefaucet specializes in faucets, shower systems, and bathroom fixtures, and every faucet we ship meets US plumbing connection standards with 3/8″ compression-compatible inlets, so the supply-line sizing in this article applies directly to our fixtures too. Our faucets are pressure-tested before shipping and backed by a limited warranty on the cartridge and finish — if you ever hit a connection you can’t match, our support team will size it with you before you buy.