Bsp npt sizing confusion

[Daniel]

Hi, I have recently purchased a bsp adapter for a npt pipe, the pipe has a 3/4" male end (thread size). The 3/4" adapter has a female opening of 1" and is obviously to large. I have received this response from the seller of the adapter...

Hi Daniel,

Thanks for your reply. I think you may have been caught out by pipe thread sizes. With BSP and NPT the size is based on bore not thread diameter, it catches a lot of people out if you are not familiar. For instance 3/4 BSP and NPT actually measure appx 1" . If you need an adaptor that actually measures 3/4" then the thread size would be 1/2 BSP/NPT

Kind regards

The bore actually measures 5/8".
Am i being duped to avoid return charges?
Many thanks in advance
Confused Daniel

 

[ShaunCorbs]

Pipe thread sizes always go up a size eg

3/4 bsp measures 1” od on threads
1/2 nap measure 3/4” od on threads

Most showers are 1/2” connections

 

[Chuck]

Am i being duped to avoid return charges?

No. Here's a useful guide to identifying BSP and NPT threads:

BSP Thread Size Guides - BSP sizes in mm | Finding the right thread size

Use our tables and free downloads to ensure you're ordering the correct parts when replacing bushes and plugs on old radiators.

www.castrads.com

 

[Daniel]

Thank you both for your help, at least i'm not being scammed!!! So with 14 threads per inch theoretically I don't need an adapter anyway. The bore is still not 3/4" anyway but I'll chalk it up as something i'll never quite get my head around!
Many thanks
Daniel

 

[Stigster]

The bore is still not 3/4" anyway but I'll chalk it up as something i'll never quite get my head around!
Many thanks
Daniel

The fitting is named after the internal bore diameter of the pipe but the fitting itself obviously has to be sized to accommodate the size of the bore plus the wall thickness of the pipe.

If you have a 1/2" pipe, the bore diameter is 1/2" but when you measure the internal diameter of the fitting, it's closer to 3/4" in size because it has to go over the pipe.

 

[steadyon]

BSP threads have a 55 degree included angle on the threads, Whitworth style with rounded crests and valleys. NSPT threads are 60 degree included angle, SAE style, with flat crests and valleys. The two thread forms are not compatible.