This adapter connects a 1" G (BSPP) female thread to a 1½" NPT male thread. It's the fitting you reach for when a G-threaded fixture needs to tie into a larger NPT supply line — main runs, bigger valve bodies, or commercial fixtures where flow capacity matters. Lead-free brass, washer included, screw-in install.
Thread Connections
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Female end: 1" G (BSPP) — parallel thread
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Male end: 1½" NPT — tapered thread
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Seal method: Washer on G side (included); tape optional on NPT side
Where It Gets Used
- Main water supply runs where a G-threaded component feeds into larger NPT pipework
- Larger shower valve bodies with a 1½" NPT inlet connecting to a 1" G fixture
- Commercial-grade plumbing installations requiring higher flow capacity
- Fixture retrofits — anywhere a 1" G female outlet needs to meet a 1½" NPT male line
Why 1½" NPT on This One
The 1½" NPT male end is the largest in this adapter range. It's chosen for higher-flow applications — main supply runs and larger valve bodies — rather than single small fixtures. If you're not sure whether you need this size or the smaller 1¼" version, check the size stamped on your existing fitting before ordering. The two are not interchangeable.
Features
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Lead-free brass — rated for potable water and drinking water systems
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Washer included — G thread seals against a flat face, not with tape; the washer does that job
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Large hex body — 1⅞" (50mm) across the flats for a secure grip with a standard wrench
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Screw-in install — no specialist tools, no cutting, no pipe replacement
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G thread and BSPP are the same standard — if your fitting is marked G1" or 1" BSPP, it matches this adapter
Specifications
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SKU: CSSL56160970
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Material: Lead-Free Brass
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Finish: Brass
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Female Thread: 1" G (BSPP) — parallel
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Male Thread: 1½" NPT — tapered
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Overall Length: 1½" (38.5mm)
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Male Thread Diameter: 1½" (Ø38.5mm)
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Male Thread Length: ⅝" (18.5mm)
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Hex Size: 1⅞" (50mm)
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Installation Method: Screw-In
Package Includes
- 1 × Adapter — 1" G Female to 1½" NPT Male
- 1 × Sealing Washer
How to Install
- Verify both sides before threading — 1" G female on the fixture, 1½" NPT male on the pipe. Check the size stamped on your fitting if unsure.
- Place the washer into the G thread (female) side first. The seal happens here, not on the NPT end.
- Hand-tighten to start, then bring it snug with a 1⅞" (50mm) wrench. Don't overtighten.
- Tape or sealant on the NPT male side is optional — not needed for the seal but won't cause issues.
- Turn the water on and check the joint before closing up the installation.
FAQ
Q) Why does the G side need a washer but the NPT side doesn't?
G (BSPP) thread is parallel — it can't self-seal, so it relies on a washer against a flat face. NPT is tapered and bites down as it's tightened, which is how it seals on its own.
Q) Is this bigger than the 1¼" NPT version?
Yes — this is the larger of the two. The male end is 1½" NPT compared to 1¼" on the other adapter. They're not interchangeable, so check the size stamped on your existing fitting before ordering.
Q) Can this be used on a main water supply line?
Yes. The 1½" NPT male end is sized for higher-flow applications like main supply runs, not just single fixtures.
Q) Is the brass lead-free?
Yes — lead-free brass, safe for potable and drinking water systems.
Q) What wrench size does this take?
1⅞" (50mm) across the hex flats on the female end.
Q) My fitting is marked G1" — is that the same as 1" BSPP?
Yes. G thread and BSPP refer to the same British Standard Pipe Parallel standard. If your fitting is marked G1" or 1" BSPP, it matches the female end of this adapter.
