Thread Number: 40064  /  Tag: Wanted to Buy Items
Imperial fittings in a metric world
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Post# 425267   5/11/2020 at 09:43 by Adam-aussie-vac ( Canberra, Australia )        

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Hey guys, Iím messaging from the land down under, my vintage BVC turbinet vacuum has a surface mounted switch and the issue with that is the electrical fittings are Imperial meaning the 15 mm is too small And 20 mm is too big, unfortunately there is no home depo around here, the closest is Guam so would anybody be able to help me out with a cable gland that has 19 mm NPT fittings?

Post# 425295 , Reply# 1   5/11/2020 at 19:15 by Lesinutah (Utah)        

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Im attaching a pic off Amazon. It looks like a coaxial cable fitting used on hooking up cable TV. If it isn't maybe a pic is needed.

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Post# 425319 , Reply# 2   5/12/2020 at 02:54 by MadMan (Chicago, IL, USA)        

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"that has 19 mm NPT fittings?"
Allow me to explain our wonderful measurement system :D

NPT (National Pipe Thread [US]) is measured by the inside diameter of a steel / iron pipe. So the measurement is sort of nominal as the inner diameter will be different for all different materials and such, while the outside diameter is constant. I think you're talking about a cable gland fitting that would screw into the electrical box. The most common size for that would be 1/2" NPT, basically, though it's meant for rigid conduit (same thread standard) or for adapters and cable gland type things. You could probably search for 1/2" cable gland. The next size up, however, would be 3/4" which is almost exactly 19mm. So your measurement is a little confusing. I'm reasonably confident what you need is 1/2" though, as the *outside* diameter of 1/2" NPT is roughly 19mm so if that's what you get when you measure the hole diameter, that's 1/2".

It's important to note that outside of the Americas, the rest of the world uses BPS (British Pipe Standard). It's also imperial, and as a matter of fact, almost identical to NPT with one critical difference: the Brits used a different thread angle. In plumbing, this makes NPT and BPS completely incompatible, as the threads are responsible for sealing. For your purpose, a 1/2" BPS pipe fitting should thread in with no issue. I'd imagine you might be able to find some sort of pipe fittings to concoct an adapter to use parts available to you. Other than that, you could get some shipping quotes from American companies, like McMaster or Grainger. It's probably expensive :(

Is this machine even made in the Americas? If not, it's probably BPS.

The ebay search below brings up some things that are not too terribly expensive, but it seems like it's either coming from the US or China.


Post# 425320 , Reply# 3   5/12/2020 at 05:55 by Adam-aussie-vac ( Canberra, Australia )        
The machine is made in Britain

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While the Electrical box the switch is mounted inside of is old enough that it goes back to when Australia are used Imperial as a measurement

Post# 425359 , Reply# 4   5/13/2020 at 01:05 by MadMan (Chicago, IL, USA)        

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I'd be surprised if it wasn't BPS. I believe you guys, as most of the world, still use BPS for plumbing. (Although they might have metric-ified the numbers, I highly doubt that the actual standard has ever changed.) Go to your local hardware store and buy a regular 1/2" pipe nipple. See if that screws into the hole correctly. Finding electrical fittings in British imperial may be harder or easier for you, I'm not sure. Again, the BPS pipe *should* interchange for NPT in this particular situation, as you're not concerned with making an absolute seal.

Post# 426549 , Reply# 5   6/6/2020 at 08:18 by Real1shep (Walla Walla, WA)        

In the US, N.P.T. for plumbing has some taper for sealing purposes. In the example given above, 1/2" electrical fittings usually have no taper, so while the threads are 1/2", the dies used to make the 1/2" threads have no taper.

It only makes a difference when you're trying to make an airtight, liquid tight seal.


Post# 426575 , Reply# 6   6/6/2020 at 16:01 by Lesinutah (Utah)        

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Compression fittings are used on tapered joints. If you go from one metal example copper to another metal or PVC you have to use a brass male coupler or fittings.
The best example is one of two places. The first is under your sink where the copper stub outs meet the on off valve for the sink. You have to have a copper fitting with compression rings on the copper and usually PVC metal braided water lines. The second is in your mechanical room. The water comes into the house and connects to the maniblock that has on off valves for all water connections. Then off the maniblock is usually red and blue pex. The have metal compression fittings. The cold water coming in has a valve and connection to the valve is brass. It has a metal ring you put a crimper tool over and compress the fitting.
I just had my final test in my plumbing class on Wednesday. I have engrained in my head my teacher from one connection to another brass is the key.
I also hooked up our swamp cooler and 2/4" compression fittings are used on the water lines.

Post# 426625 , Reply# 7   6/7/2020 at 17:03 by MadMan (Chicago, IL, USA)        

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Real1shep - electrical fittings can be either tapered or not, but usually favor tapered. The reason for this is that rigid conduit is still used, almost always outdoors, where a watertight thread seal is wanted. Of course, interior fittings like BX to box fittings are not tapered. At least, if they are, it's hard to tell.

Les - plumbing classes, eh? You a plumber now?

Post# 426637 , Reply# 8   6/7/2020 at 18:43 by Lesinutah (Utah)        

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I'm now officially second year apprentice. Once you hit end of 4th year you can become a journeyman.
Plumbers currently make more than electricians and in ten years the gap in pay will be bigger.
The electricians have 30% pass rate. I'm not sure the plumbers pass rate. I do know there are some dumb really dump journeyman plumbers. I have not met a dumb electrician.

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