MK2 3.4 1963 Radiator Drain Tap

I just received a beautiful new aluminium radiator from Alicool in the UK. Really impressed. Haven’t fitted it yet but looks good when I see the old and new side by side.

One thing they did for me was put in a 1/2" 20 TPI UNF thread to fit my drain tap. The size I picked up after a trawl through the archives.

Turns out it is not right. There appears to be at least two different types of tap. Mine is the one with the ‘remote’ bar that allows you to open the tap from the top.

Does anyone know what the size thread is for this type of tap? There are others I see which look a little more like a normal water tap. It may be I have picked up a spec that was specific to a different model.

Thanks Dave

Here is for good measure pictures of my new rad :slight_smile:

The thread is 1/4-19 BSPP.
Almost but not quite the same as 1/2-20 UNF.

This subject came up recently on the XK and pre-XK forums.

Thanks Rob. That is excellent.

I understand the differences in thread type between BSPP and UNF and that the 19 in the number above is the number of threads per inch.

Can you educate me a little on the how the 1/4 inch BSP diameter of the bolt is close to the 1/2 inch UNF? I know that it is having utilized the miracle of the internet and created this little table…

image

But what does the 1/4 actually refer to… appears to be something to do with the size of the pipe it was intended for ?

I did some research but couldn’t find an idiots guide to this topic ( lots of specialist info).

Cheers for the extra bit of education if you can :slight_smile:

Dave

You are on the right path. Pipe sizes roughly, but not exactly, correspond to the inside diameter of standard weight, Schedule 40 pipe. It is a nominal dimension, not exact. Thin wall and heavy wall pipe have the same OD but different ID as standard wall pipe but still are identified by the nominal pipe size diameter.

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