Thread converting

[Lopez Mike]

Question: Are we talking about this thread difference being the angle of the individual threads? If so, I cannot see why using a tap to modify the threads would weaken it at all.

In the case of Whitworth fastener threads, people have been running an S.A.E. tap through the holes for years. The pitch and diameter are almost all the same. Just the thread angle and the root and tip shapes are different. 55 v.s. 60 degrees and rounded v.s. squared off. The head sizes, of course are quite different.

At the pressures we run, our highest hydro tests being under 300 psi in most cases, the major loads on the fittings are not from pressure by a huge margin. Vibration and oafishness loads far exceed steam or water pressure.

Mike

[johnp]

Mike, The picture above is the water gauge I want to mount. The thread is 1/2" BSP, my boiler has 1/2" npt outlets @ 6" centres, they offer thread on or flange mount cocks. Prefer thread because of the 6" centres unless I make custom flanges. I just want to be sure that a male 1/2" npt to female 1/2" BSP brass adapter/bulkhead is the right way to do this.

[Cyruscosmo]

Hello

I did some reading online and found the fittings you would need to adapt from NPT female to BSP male. Aside from being rather expensive it looks like that would work fine. They don’t stick out a whole lot but be careful with the extra leverage; they would be easier to break off at the adapter rendering the safety ball in the site gauge ineffective.

I got a curiosity question for ya Johnp. Have you contacted the maker of that water level gauge to see if they offer it in NPT?

Cheers
Scott

[johnp]

Yes, I have contacted them. They they don't make NPT, it would be hard to line up the cocks with a tapered thread.

[Lopez Mike]

I'm missing somethings here (not unusual).

NPT is a tapered pipe thread. BSP is a tapered pipe thread. Yes? No?

Other than the different thread shape, are they a different taper?

In some far away universe far in the future these things will be standardized. Not holding my breath just yet.

Mike

[johnp]

Their description says BSP parallel thread

[Cyruscosmo]

Hey Mike

http://pipeandhose.com/node/2

It looks like they share the same taper but have different actual thread profiles. I would think a tap or die would be pretty easy to use to convert one to the other so long as you had enough material to work with.

Cheers
Scott

[Lopez Mike]

I stand corrected and educated.

A tap or die won't work for a couple of reasons. A: his gauge uses BSP parallel threads. B: The pitch is different, 11 tpi for BSP and 11 1/2 tpi for NPT. The thread shape issue I could deal with but the pitch and parallel issues are show stoppers

That's a good link. I'll book mark it for future reference. I don't know which system, BSP or NPT is weirder. Flip of a coin. All this stuff based on the length of some kings body parts can be a pain.

Mike

[PeteThePen1]

Hi Folks

Just noticed that I had not read this thread, so apologies for the late addition.

If the water level gauge cocks are new and come from a British Supplier, you could possibly ask him/her to supply them un-threaded. That way you can put on your own NPT thread as there should be plenty of metal. The existing cocks should find a ready market in the UK despite the horrendous cost of shipping these days.

Regards

Pete

[Oilking]

I believe that 1/2" and 3/4 are 14tpi in both systems. That's why it's so easy to get it wrong when dealing with those sizes.

Chasing threads

Dave