# thread pitch for Arc AAA, sae or metric?



## cy (Jul 1, 2004)

What's the thread pitch for Arc AAA? It doesn't quite fit my SAE or metric gauge. The closest seems to be 15/32 X 32tpi. .4480 is the finished diameter, measured OD on threads.

Does Arc AAA have custom sized threads?


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## gadget_lover (Jul 1, 2004)

Mine's 32tpi.

OD of the male part; .444
ID of the female part .426

That's an arc AAA premium.

Daniel


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## CNC Dan (Jul 1, 2004)

As far as I can tell it is a custom non-spec thread.


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## cy (Jul 1, 2004)

I think it's a custom non-spec thread too. I've tried every pitch guage SAE & Metric commonly available. Some are close. But none are exact. 1/2 X 32 is too big, 7/16 X 32 is too small. 15/16 X 32 apears to be the closest. No one has that in stock to compare before ordering. /ubbthreads/images/graemlins/icon3.gif


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## tvodrd (Jul 1, 2004)

A little OT here, but 15/32-32 is a semistandard _electrical_ thread with taps and dies readily available. It's used on toggle switches and other electrical applications. You can shorten, retap and bore an Arc AAA case to use an N-cell by that route. Doesn't leave much thread engagement, but it is sufficient! (The NLS) 

Larry


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## cy (Jul 1, 2004)

Larry, Where would you recommend ordering the 15/32-32 electrical thread tap & die from?

Thanks,
CY


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## PEU (Jul 1, 2004)

You can order one from http://www.travers.com/ for abour $12

I also need one, but shipping to Argentina is more expensive than the tap itself... /ubbthreads/images/graemlins/frown.gif

Pablo


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## Doug S (Sep 3, 2004)

[ QUOTE ]
*cy said:*
I think it's a custom non-spec thread too. I've tried every pitch guage SAE & Metric commonly available. Some are close. But none are exact. 1/2 X 32 is too big, 7/16 X 32 is too small. 15/16 X 32 apears to be the closest. No one has that in stock to compare before ordering. /ubbthreads/images/graemlins/icon3.gif 

[/ QUOTE ]

Hmmm..., I have some 15/32-32 stuff on hand. I tried mating with ARC head and tube. The head is a very loose fit on a 15/32-32 nut and the tube will not thread onto a 15/32-32 male part. It's rumored that not all ARC AAA stuff is threaded the same but I haven't been able to confirm this. I asked about it in this thread: ARC AAA thread differences??


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## McGizmo (Sep 3, 2004)

I have a 15/32x32 tap; used it for some prototype switch parts years ago. It will not think about going into the couple battery tubes I tried. I recall Peter fessing up a couple years ago that this was a non-standard thread. I am guessing 29/64"x20 if it is even based on fractions. It could easily be .445" or .450"x32 . If these are spit out on a CNC machine, I would think single pointing or a special ground tap would be no problem. This could also explain all of the "rejects" that ended up on the shelf and E-Bay.


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## cy (Sep 3, 2004)

Don, How might someone get a custom cut tap done? what would be the cost?


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## Doug S (Sep 14, 2004)

FWIW, I have now measured a small sampling of the black [older style] and Grey [HA newer style] heads. The black ones measure 32 TPI and the grey ones 30 TPI to the best of my measuring abilities using a steel rule and a microscope. Both have the same oddball dia of .445 +/- a few thou across the dia of the male threads.


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## McGizmo (Sep 14, 2004)

CY,
Larry has a good custom tap source. I have ordered through Rutland Tool and they use an outfit in FL tha I failed to write down. /ubbthreads/images/graemlins/frown.gif


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## cy (Sep 14, 2004)

Don, DougS, thanks for the detective work. so 32 and 30 TPI X .445 dia. 

I just counted threads on a grey HA head and I get 30 x .4440 dia. Pitch guage does fit the best using 30 tpi. 

I've got 15/32-32 which is too big (.4687 -32) 7/16 - 30 (.4375 - 30) is next to try. it apears to be slighty small. 

7/16-30 is .0075 too small, a custom may be the way to go. it may be worth ordering in one just to see if it if it's close enough.


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## residue (Sep 15, 2004)

i would be interested in finding a source for a custom tap, as well, if someone can suggest a supplier.


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## tvodrd (Sep 15, 2004)

Custom taps/dies are rather pricey. McMaster-Carr will have them ground for you on special order and the taps are around $100! (Based on a 21/32-32 I had done.) Correctly specifying them can be unfun!

Larry


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## cy (Sep 15, 2004)

Larry, thanks for the lead on who will can make custom tap. I think I have a solution using std sizes. 

I'm planing on ordering a 7/16 - 30 die. This will make a grey head .0075 smaller than the 30 pitch thread on an older series Arc AAA body. making it possible to fit a new head to an old syle body.

is 7.5 mill too much slop for thread tolarances.


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## Doug S (Sep 15, 2004)

[ QUOTE ]
*cy said:*
Larry, thanks for the lead on who will can make custom tap. I think I have a solution using std sizes. 

I'm planing on ordering a 7/16 - 30 die. This will make a grey head .0075 smaller than the 30 pitch thread on an older series Arc AAA body. making it possible to fit a new head to an old syle body.

is 7.5 mill too much slop for thread tolarances. 

[/ QUOTE ]
Cy, I had *assumed* that those heads that I measured 32TPI were older ones since they fit the bodies with the circumfrential lettering. You seem to be saying that the 30TPI are older. ??


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## tvodrd (Sep 15, 2004)

Percentage engagement is very deceptive! On the NLS, I used the 15/32-32 tap, and then bored it to fit the N-cell. There was almost _no_ thread depth left, but I haven't heard of anybody stripping one out yet! /ubbthreads/images/graemlins/icon3.gif The 5/8-32 on the CR2-II is similar but better than the NLS. Going to a buttress or acme-similar could represent an improvement. Keeping a relatively fine tpi trades off battery-crushing by the uniniated vs a quarter turn from low to high with a twistie. I'm still learning.

Larry


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## cy (Sep 16, 2004)

[ QUOTE ]
*Doug S said: Cy, I had *assumed* that those heads that I measured 32TPI were older ones since they fit the bodies with the circumfrential lettering. You seem to be saying that the 30TPI are older. ?? 

[/ QUOTE ]

My bad, the 30 tpi are the newer one's. 

The 32 tpi bodies don't seem to follow any pattern. I've seen Ha grey, black, nat, Type II black, all with 32 tpi. where the lettering is placed seems to make no difference.

The problem is the 30 tpi head will not quite screw down all the way into the 32 tpi body. I'm hoping by running a 7/16 - 30 die, it will make the heads just small enough to screw down all the way.*


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## Doug S (Sep 16, 2004)

[ QUOTE ]
*cy said:*
The problem is the 30 tpi head will not quite screw down all the way into the 32 tpi body. I'm hoping by running a 7/16 - 30 die, it will make the heads just small enough to screw down all the way. 

[/ QUOTE ]

Might work. It will be close. The heads appear to have about 4 threads. The difference between 4 threads of 30TPI and 4 threads of 32TPI is .008". Let us know how it works. I'm curious.


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## tvodrd (Sep 16, 2004)

cy, If it doesn't quite make it, try some abrasive paste (like for valve grinding from an auto parts store) and "lap" it in.

Larry


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## gadget_lover (Sep 17, 2004)

My brother worked with jewelry for a while. He suggested that you can make a very fine abrasive paste using 600 grit corum...corundu... That kind of sandpaper that begins with a C. Burn the paper and you are left with the grit. Mix with water and apply a very small amount to the threads. 

Clean very well when done. The grit will contin
ue cutting every time if you don't clean it out.

Daniel


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## Doug S (Oct 24, 2004)

I've been messing around with ARC AAA heads lately. I have a question related to this thread topic. I suppose this question is directed at folks that are knowledgible in the field of CNC production. The ARCs are using a 30TPI thread about .444" diameter, clearly an oddball size. If a standard thread such as 7/16-30 [only .006" smaller] is available, why use an oddball size? Having examined the heads closely, if can see no reason that using 7/16-30 would have created a problem w.r.t. wall thickness, etc.
Any ideas?


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## cy (Oct 25, 2004)

OK I'll fess up. I've solved the ARC AAA thread problem last week. 

We've all known for sometime that not all ARC AAA bodies would fit with all AAA heads. 

late style heads would just miss threading all the way down on old syle bodies. Old style heads wouldn't thread on late bodies at all. 

Here is what I did to solve:

posted several places, 15/32-32 tap would solve all my problems. So I ordered a 15/32-32 tap and eagerly tapped an early style body. first reject, results was pretty bad. late head would now thread down, but way too loose.

15/64 was too big, 7/16 was too small. thread guages wouldn't fit, tried metric sizes, tried sae. 32 tpi seemed to be the closest. 

It became apearent a custom thread size was used in ARC AAA. Next I hunted some custom tap and die makers. got a quote for aprox. $200 to have them custom made up /ubbthreads/images/graemlins/icon15.gif

minutes from prepaying for a $200 tap & die. I get a wild idea. I need a .4470 - 32 pitch, 7/16-32 = .4375 -32 or to small by .010in. 

final solution is purchase an adjustable 7/16-32 die for $4. then open up die far as adj screw will allow. Then take opened up die and rethread late style head. 

The opened up die cuts .4470-32 threads. You now have a AAA head that will fit either late or early bodies. 

Simple solution, but took me a while to figure out. /ubbthreads/images/graemlins/popcorn.gif /ubbthreads/images/graemlins/popcorn.gif /ubbthreads/images/graemlins/popcorn.gif


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## vortechs (Jun 30, 2006)

This thread seems to be worthy of a bump, since the topic of ArcAAA thread size just came up again. 

:bump:


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## will (Jun 30, 2006)

Many years back I was a machinist in a prototype shop. We would make 3 of these , 10 of those, all custom made stuff for the aerospace industry, some even for the lunar lander. From what I remember about measuring threads and thread depth, it is not as simple as measuring the outside diameter of the "bolt" or the inside diameter of the "nut". For example, a 1/2 inch bolt will measure less than .500. Some of the loss is atributed to the rounding of the tops of the threads. The true way to measure is to get three "rods" of a known diameter. These rods should fit inside the groove of the thread and stick out over the top of the groove. two go on the top, one on the bottom. then you measure this. Then you go to the machinist's handbook and look up the measurement. Sounds complicated. but it really isn't. For the "nut" you would have to make up a thread guage. All this is based on the standard 60 degree thread. 

I have a mini lathe in the house. I have cutdown a few mini mags and had to re-thread the barrel. I use a single point threading tool. The lathe has the ability to cut different threads per inch. the minis are 28 TPI. The easiest ( read cheapist ) way to determine TPI is with a bolt or screw of a known number of threads per inch, common TPIs are 24, 28, 30 32. The diameter doesn't matter, this is only good for a "bolt" all you do is just lay the bolt on top of the other bolt. if the TPI is the same, they will 'fit' together. if not you can see the mismatch of the threads..

Having said all that - I like the above idea - adjust the Die all the way open and go from there..

and sometimes - there is just too much information...


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