How to connect a faucet and pipe with different sizes
Supply lines and shut-off valves frequently come in mismatched dimensions, such as 3/8-inch and 1/2-inch fittings, or P-traps that don't fit standard sink drains. This dimensional conflict prevents DIYers from completing basic plumbing installations without buying specialized adapters or alternative components.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
- 1Buying a plumbing size adapter from a big box storeDid this help you?
- 2Installing a straight stop valve that adapts the connection sizeDid this help you?
- 3Returning and replacing the faucet with one matching the existing connectionsDid this help you?
- 4Using reducing bevel washers to adapt smaller tailpieces to larger trapsDid this help you?
- 5Using couplings and bushings to step down pipe sizes from the wallDid this help you?
- 6Checked multiple local hardware stores for matching threads or custom threading services.Did this help you?
- 7Buying adapters or different styles of tub spoutsDid this help you?
- 8Unsoldering or uncoupling the existing pipe fittingDid this help you?
- 9Buying a differently sized adapterDid this help you?
- 10Replacing the entire integrated valve with a standard angle stopDid this help you?
- 11Disconnecting the white hose and attempting to connect directly at the valveDid this help you?
- 12Remove the incorrect valve or angle stops and connect the 1/2 CPVC directly to the valve using proper solvent connections or ball valves.Did this help you?
- 13Replace the entire shutoff valve with a modern compression or push-to-connect fitting.Did this help you?
- 14Search for a specialized adapter to bridge the flared valve to the standard hose.Did this help you?
- 15Hire a professional plumber to handle the valve replacement.Did this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“bought a house, laundry sink wasn’t connected had hoses but the threads of the hose connector don’t meet the threads of the supply (too shallow).”source ↗
“bought new hoses still the same issue. thought connecting a few hoses would be easy.”source ↗
“Based on brief research it seems I may have a 3/8 and 1/2 inch mismatch, do I just buy an adapter or if the faucet is refundable should I get a different one.”source ↗
“I believe the p trap I have is too big for the sink drain. What would be the best way to connect this?”source ↗
“Broke first time home owner trying to do what I can but coming up short. Any help is very appreciated.”source ↗
“Basically, to summarize, the fittings in Singapore have the same sizes but the threads dont match therefore i cannot screw into the water system.”source ↗
“Ive checked about 8 stores, none have a matching thread nor can custom.”source ↗
“Not sure what to do here to connect the below system to the SG HDB water inlet and out let”source ↗
“I’m replacing my bathtub spout and want to switch to a matte/flat black tub spout with a diverter.”source ↗
“I originally bought a slip-on/set-screw style spout, but there’s only about 3/4" of plain copper before the soldered fitting, so I don’t think that style will work without redoing the plumbing.”source ↗
“I’d really prefer to leave the existing pipe/fitting alone and buy a spout or adapter that will work with what’s already there.”source ↗
“Trying to avoid buying the wrong style again.”source ↗
“I wasn’t sure how to do that with the white hose connected like this:”source ↗
“Alright so I didn't realize that the valves that are installed have 3/8 inch threaded outputs. Can anyone tell me the best way to make this valve work with 1/2 CPVC lines?”source ↗
“I intended on just using 1/2 shark bite connectors but didn't realize it was 3/8.”source ↗
“How would you go about connecting the supply line from the bathroom faucet (black) which is 3/8 to the white flexible pipe line coming from the water supply.”source ↗
“I thought the water supply line was 3/4 but I bought this 3/8 to 3/4 adapter and the water line didn’t fit.”source ↗
Where this came up
People with this problem also raised
- 14How to connect a sink drain to existing glued PVC pipes
- 29How to figure out confusing plumbing and water flow directions
- 3Why won't a new bathtub spout fit my existing pipe?
- 2Why do matching white bathroom fixtures look different in color?
- 22How to fix an off-center toilet drain during a remodel
- 126How to fix a leaking water pipe in a tight space