Morris Minor Owners Club

So I tried to figure out what thread the oil pressure switch is using but I have not found any 100% answer so far.

Some say it's BSP(T) or actually BSPP I think (would require washer), some say it's NPT, EMS's ACC203 say it is NPT in all holes, but again, many say the engine block is BSP/BSPP.

Some say it "might" be BSP but it's ok to put an NPT sensor/adapter there (I don't agree).

Brave's AI say it's BSP or NPT

Anyone know 100% sure what it is ? is it different between years or are they all the blocks same ?

I tried to find anything in the workshop manual but have not located anyting yet.

(Question is about a 1958, 948cc engine)

The thread is 1/8" x 28 TPI BSP. Early switches are parallel thread and need a washer to seal. All the modern switches seem to be taper thread. They do not screw all the way in and do not need a washer to seal.

Stephen

I have measured the threads in the block and on the switch with both a tap and die nut and I find that they are 1/8" x 27 tpi NPT.
If you have a taper thread switch or adapter they will both screw into either a NPT or BSP parallel thread.
The taper thread does not go fully home into the female parallel thread. Do not overtighten as there is a possibility that the tread will shear if you do.
The majority of threads and their sizes are shown in the Mechanical section under 'Thread Sizes'.

Just as a generalisation.
Npt and Bsp threads have a different crown, that is the form of the thread at its peak or top is different.
A thread called a "uni-thread" was invented in the 1980's that accommodated both types giving a form of interchangeability, it did not catch on as it wobbled its way in both bsp and npt female threads, utilising a copper washer to seal.
It just did not feel right.
Any fitting needs to screw in more than the 1-2 threads you will achieve if you try to marry npt with bsp.
Having ascertained the correct thread you will find the female is parallel, a taper thread male with a little thread tape will do the job.
A sealing washer will not be necessary with taper male to female parallel, your female thread will not be taper, it will be parallel.
I fitted an oil pressure gauge kit with no real issues, it came from ESM complete with fittings.
I assume this is your intention.