Post Number: 1925
|Posted on Thursday, 02 June, 2016 - 05:01: |
I am having one of those days where my head is swimming with regard to what I might have known once, but has somehow slipped away.
I wrote a brief article, Building a Hydraulic Pressure Test Gauge (B.Vogel) several years ago now. One of the parts I listed is a 1/4" NPT (external/male) to 3/8"-24TPI (internal/female) reducer that I used to screw the brake hose part into the tee since I didn't really need a seat there (though it wouldn't have hurt to have had one). In that article I gave a direct link to a website that used to sell this thing, but when you click through on it now it takes you to a 3/8 NPT x 1/4 NPT Reducer Bushing.
Now I know that the tee itself, and all the things that screw directly into it, are 1/4" NPT. I know that the things that screw into the adapters that screw in to the tee all have 3/8-24TPI thread.
So, since the external side of these adapters are 1/4" and the things that screw into them are 3/8"-24TPI, that means that the 1/4" and 3/8" cannot refer to outer diameters, since 3/8" is a greater diameter than 1/4" and that doesn't work given the actual configuration.
What do the 1/4" and 3/8" refer to in the context of these fittings?
Also, if I were looking for an adapter that was 1/4" NPT Male to "will allow a standard brake hose for our cars to screw into it" female what would the appropriate search terminology be? I'm not finding anything what I think it should be and I know it had to have existed when I put this thing together in the first place.
I realize that one can get around this entirely just by making two of the "custom" adapters that I describe making for the bleed screw, but I'd still like to get this all straightened out in my head.
richard george yeaman
Post Number: 510
|Posted on Thursday, 02 June, 2016 - 08:51: |
Hi Brian I have had one of those days also my brain hurts. I think if you could find Robert Noel Redington He would know this information chapter and verse. I have read your post again and my brain hurts even more.
Post Number: 1926
|Posted on Thursday, 02 June, 2016 - 09:22: |
There's definitely no rush on getting the answer. But this kind of stuff is generally most easily explained by those who "know it in their bones" because they've had to use it constantly in their professional lives.
RNR, AKA Bob_UK, might know this that's for sure.
richard george yeaman
Post Number: 512
|Posted on Thursday, 02 June, 2016 - 09:58: |
Brian the UK refer to pipe threads as BSP British standard pipe instead of NPT and also we are metric instead of Imperial and probably American inches are different as well. (my head still hurts).
Post Number: 91
|Posted on Thursday, 02 June, 2016 - 10:08: |
Brian, I feel your pain. I just machined my own tee with two female 3/8-24" threads to fit brake lines with bubble fittings and one female 1/4" NPT thread to fit a gage. I did this because I couldn't find what I needed even at McMaster-Carr - which is the greatest site in the whole WWW.
The confusion regarding NPT threads lies in the fact that Pipe sizes (and their corresponding thread sizes) are based on the internal diameter of the pipe. Bolts and tubing are based on their outside diameters. A 3/8" bolt will actually measure just under .375 and a 3/16" brake tube will measure .187.
Where it gets confusing is that the id of 1/4" pipe is nowhere near 1/4" anymore. 1/4" pipe means that it has an internal diameter of at least 1/4". I just measured a couple of examples I have laying around and the id's are closer to .350.
I have been working with pipe threads for more than 30 years and it is still sometimes difficult to guess pipe size without measuring tools if it is out of context.
For all practical purposes, a 1/4" NPT thread might as well be named Steve because the size isn't particularly relevant anymore.
I might suggest that one could obtain pipe plugs in the following sizes and label them for future reference: 1/16", 1/8", 1/4", 3/8", 1/2" and 3/4". That'll be easier than trying to guess at a pipe size in the wild.
Post Number: 1927
|Posted on Thursday, 02 June, 2016 - 10:39: |
Well, the offerings so far have given me great comfort. I thought, "Oh, I must have known how this worked when I put this together!," but what I now realize is that I carried the various bits that I had along with me to find the various bits I needed by trial-and-error when necessary.
It's not like there are so many parts involved that this was not practical. It was only when I got private correspondence from someone saying that they could not find a 1/4" NPT male to 3/8-24TPI reducer that this all came up again. I know that, at the time, I purchased that reducer "off the shelf" but cannot find any receipt for same (which means it was a "brick and mortar" find, probably at Fastenal.
To invoke La Streisand: "What's too painful to remember, we simply choose to forget!"