Help: odd sized pipe thread needed

[IslandTractor]

Hi folks,

I need to identify a source for a roughly three inch pipe nipple and female/female connector with the following dimensions:

Major OD 0.625 inches
Min OD 0.555 inches
Threads per inch: 16

These are the measurements of a oil breather cap on my Caroni flail mower gearbox. I need to build an extension to keep the oil from oozing out (the gears throw it against the cap and it oozes quite a lot...the extension will hopefully keep that from happening). The gearbox is Caroni built (Italian).

I have found measurements for 3/8 inch NPT (0.675 OD, 18tpi) and for BSP 3/8 pipe (0.625 OD, 19 tpi) and have tried both but neither fit. I cannot figure out what other measuring convention Caroni is using. I have measured the threads directly and also compared them to a thread gauge and it is really 16tpi not 18 or 19. That is pretty darn close to 1.5mm thread pitch and given that the gearbox is made in Italy perhaps there is a metric pipe system that would match. Anyone have experience or suggest a source?

Thanks

 

[randy41]

i would try metric fittings...google it

 

[IslandTractor]

i would try metric fittings...google it

I've been trying. No joy. Perhaps I am using the wrong search terms. I've tried "metric pipe thread 1.5mm" and a few variations. I get a variety of hits but nothing similar to what happens if you put in similar terms for US or Bristish measurement systems. Any thoughts?

 

[davkir]

McMaster-Carr has a lot of this kind of stuff and their catalog (also online) has all sorts of interesting tech. info.

 

[tommu56]

here is a couple of links

British standard
British standard pipe thread - Wikipedia, the free encyclopedia

national pipe

National pipe thread - Wikipedia, the free encyclopedia

cross from national pipe to DIN size
NPS - "Nominal Pipe Size" and DN - "Diametre Nominal"


tommu

 

[Sherweld]

Try this
THREAD IDENTIFICATION CHART -- PART 1

 

[638]

What you have is "11/16-16NS". This is a special thread, and is listed on my thread chart. This thread would be easier cut on a lathe than trying to find a tap and die set. I've worked with odd threads off & on for fifty some years and have never ran across this one. Good luck.

 

[DieselPower]

I'll have to check when I get home. I might have that tap and die size. I have most but not all of the national special tap's and die's under 1 inch. Post back later or tomorrow to let you know if I have it. Would be more than happy to mail it to you to use if I have one.

 

[3RRL]

Island,
Is the number of threads exactly 16tpi? (perfect fit or not)?
If not, I'll bet it's a M16x1.5 Metric thread.
Do you have a Metric thread gauge?

 

[IslandTractor]

Thanks to you all for your suggestions. Here is where I stand after a few hours of internet research and direct measurement: I have looked at the various websites you guys have provided. It makes for some fascinating reading, especially one article I came across that discussed how these American (SAE), British (BSP) and German (DIN) systems came into use. (Believe it or not apparently some of the confusion was intentional on the part of the Brits to make sure the Germans could not easily find substitute parts for captured British weapon systems!!). There is even a "unified" screw thread system designed in the US that seems to be used for bolts but not pipe fittings.

However, back to the practical issue at hand: I think I have narrowed down what I need to one of two thread sizes both of which appear to be practically unobtainable from the big web sources in the USA. The two possibilities are either a British sized 3/8 inch with 16tpi which is called Unified Coarse thread (note different OD and standard 18tpi for SAE). The second possibility is a DIN 10mm pipe with 1.5mm thread pitch. I cannot find any reference that lets me cross check those DIN measurements with the 0.625 Major OD and 0.555 minor OD in inches.

I have used a paper thread gauge and also directly measured the threads of the cap. The 16tpi thread gauge matches perfectly (holding the cap threads directly over the paper print out and sighting down to see the match). The cap threads also line up perfectly with 1/16 inch ruler segments. However, the 1.5mm thread pitch is also extremely close and I could not differentiate which was closer using the thread guage (1/16 inch and 1.5 mm are awfully close as measurements).

I am therefore thinking that either thread pitch would work so I need to match the major and minor OD figures. That is what I have had trouble locating standards for with the DIN and Unified coarse thread. NPT 3/8 is clearly too big. The BSP 3/8 is exactly correct at 0.625 OD but the BSP thread count is 19tpi not 16 so I know it is not a BSP standard.

Again, the other big issue is that I have not been able to locate any US supplier for the DIN or Unified Coarse thread pipe fittings. I tried McMaster Carr and two or three others. I don't have their catalogs so I had to use the websites which can be difficult. Maybe I missed something. I need a 3 inch pipe nipple with threads on both ends and a matching female/female connector. I was thinking of calling McMaster Carr in the morning but this is such an arcane matter that I kinda doubt the guys on the order desk will know...still worth a try.

Again, thanks for your suggestions. I will post a follow up when I have more info.