# 5-40 tap and die set



## TarheelTom (Apr 8, 2010)

On Elmer's Tiny plans, he specifies a 5-40 thread on the steam inlet pipe.

Is this a 5-40 NC thread, or a 5-40 MPT, or some other type thread?

Who has the taps and dies?

Thanks

Tom


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## arnoldb (Apr 8, 2010)

Hi Tom

That would be a 5-40 MPT. 

If you cannot find the taps, you can use just about any suitable size close to it. Metric M3 would work well for example. 
And if you find any taps hard to come by, you can just drill the hole slightly oversize and turn up the steam connector to be a press fit in it instead of threading. And if you have problems turning for a press fit, loctite will also work. In fact, last year when I built my version of Tiny, that's what I ended up with.

Regards, Arnold


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## TarheelTom (Apr 8, 2010)

Thanks, Arnold.

tom


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## cobra428 (Apr 8, 2010)

Can you just make it 3/16-40 MPT? Lot easier that looking for hens teeth :big:

Tony


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## GailInNM (Apr 8, 2010)

Tom,
On the Tiny, there is nothing very sacred about the 5-40 thread. A regular 5-40 NC will work just fine. Many of the hardware stores, such as ACE, have 5-40 taps and dies, as do many auto supply stores that sell tools. You may have to grind off the tip of the tap to get it to give you enough threads.

You could also use a 4-40 thread if you have a tap and die for it. If you do, it would probably be best to reduce the hole in the steam inlet from 1/16 down to 3/64 or if you are using number drills any thing from #55 to #60. The Tiny does not take much air so the hole size is not at all critical. 

If your threaded connection leaks air, a turn of plumbers Teflon (PTFE) tape around the thread will take care of it, but it probably won't leak.
Gail in NM


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## BigBore (Apr 8, 2010)

This brings up a couple of things I need cleared up in my head. Is MPT and MTP the same? Second, where does it say that Elmer's plans call for the MPT or MTP and not the UNC? Are Rudy's also like that?

The reason for the questions is that I have been looking for small taps that show up as "A Deal!" I just want to be sure that I looking up the right tree.

Ed


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## rake60 (Apr 9, 2010)

The straight 5-40 thread is still very conman in the gunsmiths craft.
Taps and dies can be found in those venues.

I don't use them myself. I use the closest metric size, since that is what
my hobby tap and die set happens to be.

Rick


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## GailInNM (Apr 9, 2010)

Ed,
I don't think Elmer ever specified a tapered thread on any of his engines. 

MPT and MTP are completely different thread systems.

MPT and FPT are a commonly used subset of the National Pipe Taper (NPT) such that MPT is the same as saying Male National Pipe Taper and FPT is the same as saying Female National Pipe Taper. These are the fittings that you use for regular plumbing and the size designation is much different than the actual size of the pipe. For example a 1/4 inch NPT pipe measures about 0.54 OD and 0.37 ID.

MTP stands for Model Taper Pipe. The designation is not part of any standards organization that I know of but over many years of usage and evolved into a more or less standardized set of threads. With MTP the size designation is the actual size of the pipe or tube, that is 1/4 -40 MTP pipe is actually 1/4 inch diameter. There is one common size between the two systems and that is 5/16 MTP has the same specifications as 1/16 NPT. 

Here are a couple of links that may help.
http://www.pmresearchinc.com/store/home.php?cat=38
http://www.nelsonslocomotive.com/Shay/Plumbing/PlumbingI/PlumbingI.htm

Note that there is a error in the chart on the second link. It shows 1/4-40 MTP as the size for 5/16 tube and that is in error.

Gail in NM


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## Deanofid (Apr 9, 2010)

BigBore  said:
			
		

> The reason for the questions is that I have been looking for small taps that show up as "A Deal!" I just want to be sure that I looking up the right tree.
> 
> Ed



Ed, when you look for those that are like you say, "A Deal!", if they are made of carbon steel, they're NOT. If they're the bottom of the barrel of any type, they're not a deal either.

Don't skrimp on taps. Broken end mill; put in another one and continue. Broken turning bit; put in another one and continue. Broken tap; wailing and gnashing of teeth. A hole in your project with a piece of very hard metal stuck fast. Hand wringing and impolite words ensue.

Buy good taps.

Dean


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## BigBore (Apr 9, 2010)

Thanks for the concern, Dean, but I've got the cheap tap mantra buried deep in my head. You guys are religious on that issue! Amen! USA...HSS...all the way. So a deal will be a deal on the right stuff. Thanks for keeping an eye on me.

Gail, thanks. I really have not been "seeing" and differentiating between the MTP and the MPT. It's just an attention to detail issue. I *will* notice the distinction from now on. Thanks. And I also, have not seen Elmer make the distinction of a specific thread standard. I was assuming, as I have with all the builds I've documented here, that the author is calling out a _Unified Thread_.

Thanks y'all

Ed


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