What Size Thread on Basin Taps

Why Thread Size Matters

What size thread on basin taps? I learned this the hard way while helping a friend replace his bathroom tap. He bought a British G1/2 tap. When he tried connecting it to an American NPT fitting, water leaked everywhere.

The problem? Different countries use completely different thread standards.

This guide shows you exactly how to identify the right thread size for your basin tap. No plumber required.

Thread Standards by Country

Europe and UK: G-Type Thread Territory

Europe and the UK use G-type (BSP) threads as standard.

These are parallel (straight) threads with a 55° angle. They rely on rubber washers and PTFE tape for sealing.

The most common size for basin taps? G 1/2 with these specs:

• 20.955mm outer diameter
• 14 threads per inch
• 1.814mm pitch

America: NPT Tapered Threads

America uses NPT tapered threads instead.

These have a 60° angle and a 1:16 taper. They seal through metal-to-metal contact when tightened.

Their basin tap standard? 1/2" NPT:

• 21.336mm outer diameter
• 14 threads per inch
• 1.814mm pitch

My American friend once tried fitting a US tap in his London flat. The threads locked after two turns and stripped when he forced it.

Asia: China and Japan's Subtle Differences

China uses the same G-type parallel threads as Europe.

Japan uses PT tapered threads (55° angle like G but with taper like NPT).

This means a Chinese G1/2 tap might screw into a Japanese PT fitting but will leak. The straight vs tapered design creates tiny gaps.

International Thread Comparison Table

Thread Type	Country	Outer Diameter (mm)	Threads per Inch	Angle	Tapered?
G 1/2	UK/Europe/China	20.955	14	55°	No
1/2" NPT	USA	21.336	14	60°	Yes (1:16)
PT 1/2	Japan	20.95	14	55°	Yes

How to Measure Thread Size: 3 Simple Steps

Don't guess — measure. Here's how in 3 simple steps:

Common Questions (FAQ)

Q: Can I mix G1/2 and NPT1/2 threads?

A: No. They'll start to screw together but will never seal properly. The 5° angle difference causes leaks every time.

Q: My old tap has no markings — how do I identify it?

A: Follow these steps:

1. Check for taper (UK/China = parallel, USA/Japan = tapered)
2. Measure diameter (20.95mm = 1/2", 26.4mm = 3/4")
3. Count threads per inch (14 = 1/2", 11 = 3/4")

Q: What should I check when buying an imported tap?

A: Always confirm the thread type in the product specs.

• European imports = G1/2
• American imports = NPT1/2
• Japanese imports = PT1/2

Buy a conversion adapter if needed. G to NPT adapters are widely available on Amazon.

Summary: Choose the Right Thread, Save Years of Hassle

Getting the right thread size isn't complicated when you know what to look for.

Remember these three rules:

1. Europe/UK/China = G1/2 (parallel, 55°)
2. USA = NPT1/2 (tapered, 60°)
3. Japan = PT1/2 (tapered, 55°)

Measure the diameter, count the threads, check for taper. You'll never buy the wrong tap again.

Next time you replace a tap, measure the threads before ordering. Don't let a 5mm difference ruin your renovation. This is the core answer to "What size thread on basin taps?"