What is the thread on an oil pressure gauge?

[gmharris]

What is the thread on the fitting on the back of the oil pressure gauge of a '63 WM300? It looks like pipe thread, but I wasn't comfortable with the way a brass fitting was threading in. Before I mess up the threads, I thought I would ask.

Sorry if this question has been asked before. I wasn't able to find a previous post on this site.

[JimmieD]

Sorry for a late reply and sorrier still that it's not much help, but far as I know all mechanical oil pressure gauges use flare fittings, far different from pipe thread size.

There's 1/8", 1/4", 5/16" & 3/8" flare fittings commonly available and I find the nomenclature beyond confusin'. What appears to me to be a 3/8" flare nut is called a 1/8" flare connection! Apparently it goes by the size of the tubing, having nothing to do with flare nut size?

From that, I've never seen an oil pressure gauge that used larger than 1/4" flare, so that at least narrows the choices down to 1/8" & 1/4", and I believe they're most often 1/8".

In 45 years of playing with that type of plumbing I have accumulated a coffee can brimming over full of spare brass fittings. I think once in 1964 I happened to have the correct fitting I needed in that can. Otherwise they are something to occasionally pour out, inspect, marvel over and reinstall into container.

[gmharris]

3/16" Flare Fitting Seems to Work

Thanks Jimmie for the input.

I made the rounds of auto, hardware and hose supply stores and was unable to come up with a fitting for the back of the oil pressure gauge on my FFPW.

I eventually tried Osh Hardware. Surprisingly, Osh had a fairly complete supply of brass hardware. I found a 3/16" flare fitting which seemed to work. Osh even had a 1/8" flare fitting. The other stores had nothing smaller than 1/4" flare.

Anyway, the fitting will work, but I'm not entirely comfortable with the way it threads in. It just doesn't seem to go in without binding and it doesn't seem to bottom out. But, it's close enough until I find a used oil line with fittings.

The brass fitting is soft enough that I'm not worried about messing up the threads on the steel gauge fitting. I transitioned to a 3/16" compression fitting to attach some 3/16" tubing.

[Charles Talbert]

NAPA has the correct fitting, I have a part# at the shop if you need it.

[gmharris]

Correct Part Number

Charles:

I would appreciate getting the part number. It would probably be a benefit to a number of us.

NAPA was one of the places I went to without success.

Thanks

[Charles Talbert]

Charles:

I would appreciate getting the part number. It would probably be a benefit to a number of us.

NAPA was one of the places I went to without success.

Thanks

42x3 & 66x2 are the 2 numbers I have written down. These are weatherhead fittings, my store has a large cabinet of various brass fittings. This is the numbering system used by the weatherhead co. The same number system may be good at other suppliers who carry the weatherhead line also.

[gmharris]

Thanks Charles.

The "42X3" Weatherhead number appears to provide the answer. In looking online, that number is for a brass 3/16 SAE 45 degree flare union. The 45 degree flare is commonly used in instrumentation, refrigeration, power steering, hydraulic and pneumatic systems.

The flare fitting I was trying to use is a 37 degree flare. The 37 degree flare was developed to provide better sealing than the 45 degree flare, but is incompatible with the 45 degree flare.

I haven't really seen a Power Wagon oil pressure gauge line, but it probably uses two captive 45 degree fittings with 45 degree inverted flares on each end of the tube. That would be the same as many other applications I have seen.

[tintoptexan]

McCoy

I just finished re-plumbing my 48 B1 PW and the old line had a ferrule fitting on a 3/16 line. I went back with the same and it did not leak and works fine. I don,t know if it is the factory way, but like I said, it don"t leak. Hope this helps. Joe

[im02crazy]

UPdated with added weatherhead #'s

Thought this might help others seeking the same info for the oil line block to tubing connector. 68x3 is the 1/8 NPT male to 3/16 flare tubing connector. see attached pic