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Tap for 1/2-18?


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So some people may think this is a stupid question, but bear in mind that I have never threaded metal before.

 

I recently purchased a fuel rail from pallet in hybridz but the ends are not tapped for the hose barbs.

I believe the hose barb threads are 1/2-18nc, which seems to be the same thread for the fittings at my local home depot and the an to npt fitting I have.

The problem is that I am unable to find a tap and die kit with a 1/2-18 tap included (or just the 1/2-18 individually), all are either 1/2-13 or 1/2-20.

 

What should I do, what options do I have?

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Firstly I'll admit I know next to nothing about fuel rail fittings. But I got curious and did a quick search. Found this on AN threads: http://en.wikipedia.org/wiki/AN_threadhttp://en.wikipedia.org/wiki/AN_thread

The AN size 8 shows 1/2-14 NPT (pipe thread), but I don't know if AN 8 is the size you have.  As a place to search, I went to Amazon. They list individual taps for both 1/2"-18 (I think SAE although it doesn't say) and 1/2"-14 NPT (pipe thread). If what you have is NPT you should be able to see a slight taper to the thread. Or put a caliper on the thread to see if the thread is tapered or straight. Amazon also shows a tap for 9/16"-18 which is shown for AN 6 size. I don't know if any of this makes sense or helps. Maybe someone who really knows fuel rail fittings will join in here.

 

As bananahamuck said, an industrial supply place should have individual taps in the size you need if you don't want to wait for mail order. MSC is an online source always recommended by amateur machinists: http://www1.mscdirect.com/eCommerce/NavigationServlet?cm_mmc=Didit-_-SEM-_-ItmDtl-_-PypClk&002=2167139&004=2162606824&005=308856351&006=16904160664&007=Search&mkwid=sNF0Nn9FX&pcrid=16904160664&cid=ppc-google-Brand+Core They have everything imaginable.

 

Len

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I think you are confusing bolt sizes with sizes for pipe fittings.

 

Pipe fitting sizes are based on the inside diameter of a piece of thick walled steel pipe, like a water pipe. 

Here is a picture of four pipe taps, with a short 1/2 wrench for reference.

PipeTaps.jpg

The pilot hole you drill for a 1/4-18 NPT (National Pipe Taper) is actually bigger than the pilot hole you drill to thread a 1/2-13 bolt.

 

Both 1/4, and 3/8 pipe fittings are 18 threads per inch.   The pipe fittings on Datsun engines are not American sizes.  Datsun uses British standards, and they are different.

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The pilot hole you drill for a 1/4-18 NPT (National Pipe Taper) is actually bigger than the pilot hole you drill to thread a 1/2-13 bolt.

 

Both 1/4, and 3/8 pipe fittings are 18 threads per inch.   The pipe fittings on Datsun engines are not American sizes.  Datsun uses British standards, and they are different.

 

 

Ok, this makes sense.

 

How do you measure npt threads? I already know it's 18 threads.

 

Here's what I need to tap:

 

UP1Ef.jpg

gMEDx.jpg

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I think you are confusing bolt sizes with sizes for pipe fittings.

 

Pipe fitting sizes are based on the inside diameter of a piece of thick walled steel pipe, like a water pipe. 

Here is a picture of four pipe taps, with a short 1/2 wrench for reference.

PipeTaps.jpg

The pilot hole you drill for a 1/4-18 NPT (National Pipe Taper) is actually bigger than the pilot hole you drill to thread a 1/2-13 bolt.

 

Both 1/4, and 3/8 pipe fittings are 18 threads per inch.   The pipe fittings on Datsun engines are not American sizes.  Datsun uses British standards, and they are different.

BINGO!!!!!!!!!!

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Ok, this makes sense.

 

How do you measure npt threads? I already know it's 18 threads.

 

Here's what I need to tap:

 

UP1Ef.jpg

gMEDx.jpg

It looks like a 1/4 NPT barb from what I can tell. The others that you have in the rail look to be 1/8 NPT. And once you get it figured out change it over to AN fittings.

It will look way cleaner. 

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The easiest way to "measure" NPT threads is to just try it.   Because it is tapered, the more you tap, the deeper the fitting will go together.

According to my chart, a 1/4-18 NPT threaded hole starts out with a 7/16 straight hole.  A 3/8-18 NPT threaded hole starts out with a 9/16 hole.  

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Here is a chart of NPT info which gives approx. depth of threads:

 

http://www.engineeringtoolbox.com/npt-national-pipe-taper-threads-d_750.html

 

I don't think the thread depth is critical, so long as you don't go so deep that the hex part of your fitting comes up against the flat part of the rail. I assume the rail is aluminum. You probably need some sort of cutting fluid to cut a smooth thread and help clear the chips as you cut. Anyone have a recommendation for a fluid? Industrial supply places will have a special aluminum taping fluid, hopefully in a small can. WD40 might be better than trying to tap it dry, but somebody may know of a better solution that is easy to find. When you tap, you need to back the tap up pretty often. Maybe every 1/2 turn? You can even back the tap all the way out and blow the chips off of it and blow them out of the hole. Chips jammed in the tap result in a rough, torn thread. If you can find a scrap piece of aluminum you could drill and tap a couple of practice holes before going after your rail. You might take time to Google for "tapping aluminum". There may well be some things you should know that I'm not remembering. I'm not even absolutely sure the drill size on the charts is the same for aluminum as for steel. For a taper thread it is maybe okay.

 

Take your fitting to a good hardware store or industrial supply and they should be able to screw it into a pipe fitting and tell you what size thread it is. I don't know if Home Depot type stores will have anything sized that small, but they might.

 

Len

 

 

 

 

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I have never tapped with a fluid... Tapped with grease to avoid any chips falling into the exhaust mani above a turbo... 5 for 5 so far... and those where all NPT.

Thanks for posting real world experience. One thing with aluminum, there are a bunch of different alloys which machine differently. I think I've tried tapping and turning some pretty soft alum. which doesn't work well no matter what fluid or technique is used.

 

Len

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You guys have pitched in some real solid info, thank you for that!  :rofl:  I've got some oil for drilling metal, would that work pretty well as a tap fluid? And as for grease, what type of grease?

 

I was just talking to my dad. He gave me some of his spare AN fittings  :w00t:  

I'm going to try my local baxter's auto parts tomorrow for npt taps and more AN stuff since home depot and harbor freight did not have pipe taps.

 

5qUTa.jpg

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