TruDesign Skin Fitting / Ball Valve Thread Sizes

[Manyata]

Any help please. I just can't figure this out

Situation ...
I have an existing skin fitting (TruDesign) - which has none TruDesign Sea Cock and fittings attached. I want to change these fittings for a TruDesign Ball Valve, Load Collar and Hose Tail. The thread measures about 26.2mm across the thread (call it 1" given my dodgy measuring!).

My problem ...
Which TruDesign Ball Valve do I order ? Logic tells me I need the 1" Ball Valve - but the thread on that appears to be 3/4" according to their spec documents. Clearly I need thread on the ball valve to be 1". Is this something to do with BSP naming of threads ? I found somewhere that a BSP 3/4" actually has a thread of 1".

I am so confused - and probably thick - so apologies.

Can anyone help ?

Thanks, Tim

 

[Tranona]

The threads are exactly the same as metal valves and fittings - all BSP. The sizes are the diameter of the bore - commonly 3/4" for engine and toilet intake and 1 3/4" for toilet outlet. Sometimes 1" for larger engine intakes. So measure the bore of the valve/fitting you are replacing.

 

[Boater Sam]

BSP threads are sized on the clear bore internal diameter. So the outside thread diameter is always a good bit bigger than the size would suggest. If it measures around an inch OD then it is 3/4" BSP.
This is explained here BSP Thread Sizes Explained