1" G Thread (BSPP) Female to 1 1/2" NPT Male Adapter - Lead Free

If your fixture ends in a 1" G (BSPP) female thread and the pipe you're connecting it to runs 1 1/2" NPT male, this is the piece that bridges the two without cutting into your existing plumbing. It's cast from lead-free brass and comes with a washer already sized for the G thread side.

Thread Types

Why This Combination

A 1 1/2" NPT male end is larger than the standard 3/4" or 1 1/4" sizes in this range, so it's typically used where higher flow matters — main supply runs, larger shower valve bodies, or commercial-grade fixtures feeding into a G-threaded component.

What's In The Box

• 1 adapter (1" G female × 1 1/2" NPT male)
• 1 sealing washer

Build Details

Fitting It Together

1. Check both ends against your existing pipework before threading anything in — 1" G female on one side, 1 1/2" NPT male on the other.
2. Set the washer into the G thread side first. That's where the seal actually happens, not on the NPT side.
3. Thread by hand, then bring it up snug with a wrench sized to the hex.
4. Tape or sealant on the NPT threads is optional, not required for the seal.
5. Turn the water on and check the joint before you call it done.

Common Questions

Why does the G side need a washer but the NPT side doesn't?
G (BSPP) threads run parallel and can't seal on their own, so they rely on a washer. NPT threads taper and bite down as they're tightened, which creates the seal on that end.

Is 1 1/2" NPT bigger than the 1 1/4" version you sell?
Yes — this is the larger of the two. Double-check the size stamped or labeled on your existing fitting before ordering, since they're not interchangeable.

Can I use this on a main water line, not just a fixture?
It's suited to that — the larger NPT end is generally chosen for higher-flow or supply-line applications rather than a single small fixture.

Does the brass contain lead?
No, it's lead-free brass, suitable for potable water.

What if my thread is G 1" but slightly different from BSPP?
G thread and BSPP refer to the same British Standard Pipe Parallel standard, so if your fitting is marked G1" or 1" BSPP, it should match.