# Tapping for 10-32



## oskar (Jul 5, 2018)

I do a fair amount of 10-32 tapping on aluminum and it’s a hard going. I use a 5/32” drill which came as a set with the tap but I wonder if another drill size may do the job faster

As an example I also tap a lot of M5 and I was using #19 drill which was also a hard going but I discover from a thread in another forum that an 11/64’ drill is much better and in it is.

Is the 5/32” drill the best for 10-32 tap?


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## WarrenP (Jul 5, 2018)

You can always try one size larger , 3/16, and see what you think. Seems aluminum shouldnt be to hard to tap though.. but the extra room would probably make it easier, should still get good threads... only 1/32 inch differece. Have you tried a little wd40 while tapping?


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## pacifica (Jul 5, 2018)

It will depend on how much distance you need between the root and crest. How much pulling force will be on the threads?

Definitely with 6061  aluminum there is a point where too shallow of threads is a failure issue. 

Try a #20 drill?


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## T Bredehoft (Jul 5, 2018)

Starrett's tap and drill card (which every one of us should carry in his shirt pocket,) says the tap drill for a 10-32 screw is a No. 21, .159  diameter. 5/32, .156, is just a bit tighter,  Always use a lubricant when tapping, even if it's beeswax.  (No 20 is .002 larger yet).


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## Dan_S (Jul 5, 2018)

A #21 drill is what is recommended for 10-32 and that only 0.0027" bigger than 5/32".  I'd recommenced a good spiral point H3 class tap before a new drill.


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## markba633csi (Jul 5, 2018)

#21 drill (0.159") is spec for 10-32 
5/32 is 0.156" which also works fine for aluminum.  
For steel I would stick with #21 or even #20


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## benmychree (Jul 5, 2018)

Dan_S said:


> A #21 drill is what is recommended for 10-32 and that only 0.0027" bigger than 5/32".  I'd recommenced a good spiral point H3 class tap before a new drill.


Use a spiral point tap only if it is a through hole, as the tap forces the chip forwards in the hole, and would likely jam up if used in a blind hole; if it is a blind hole, use a spiral fluted tap, which ejects the chip out through the flutes.


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## T Bredehoft (Jul 5, 2018)

Note that a SPIRAL POINT tap drives the chip ahead of it, while a SPIRAL FLUTE tap pushes the chip behind it.  SPIRAL is not the key word. POINT points the chip ahead, FLUTE flutes the chip behind.


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## Dan_S (Jul 5, 2018)

benmychree said:


> Use a spiral point tap only if it is a through hole, as the tap forces the chip forwards in the hole, and would likely jam up if used in a blind hole; if it is a blind hole, use a spiral fluted tap, which ejects the chip out through the flutes.



That's not completely true, people have used spiral point taps for everything for longer than I've been alive, specially in home and small job shops. I have both types in my shop, but that's not a luxury everyone can afford.  My personal preference is YG spiral flute bottoming taps, but those aren't cheap.


However, I recommended a spiral point tap, because he doesn't mention how he is tapping the hole. If he is power tapping or  using a tapping guide then either type is fine, but if he is tapping by hand with no guide I would not recommend a spiral flute tap, its to easy to break.


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## benmychree (Jul 5, 2018)

T Bredehoft said:


> Note that a SPIRAL POINT tap drives the chip ahead of it, while a SPIRAL FLUTE tap pushes the chip behind it.  SPIRAL is not the key word. POINT points the chip ahead, FLUTE flutes the chip behind.


I believe that is what I said in my post -----


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## mikey (Jul 5, 2018)

I would use a roll tap for this - no chips, stronger  threads.


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## francist (Jul 5, 2018)

I would also suggest using a good-quality tap. It doesn't need to break the bank, but something better than hardware store variety. I can buy Norseman taps here as well as Widia (sp?) from my local industrial supply in the individual sizes I use frequently. Using one of them compared to my El-Cheapo Canuck Tire "104 piece set" that I purchased years ago is night and day. Cheaper taps (and dies too for that matter) just don't cut as nicely and it's really noticeable, especially in smaller sizes where you're already concerned about maybe breaking one. 10-32 in aluminum should not be an effort. And yes, some form of cutting fluid (kerosene, WD40, cutting oil, etc) will also ease the process.

-frank


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## Tony Wells (Jul 5, 2018)

WarrenP said:


> You can always try one size larger , 3/16, and see what you think. Seems aluminum shouldnt be to hard to tap though.. but the extra room would probably make it easier, should still get good threads... only 1/32 inch differece. Have you tried a little wd40 while tapping?



3/16" is approximately the major diameter of a #10 machine screw. A 10-32 tap would barely scratch it, even if it drilled perfectly on size.


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## MarkDavis (Jul 5, 2018)

My tap chart contains the following information for 10-32 cut threads.
Drill size...…………………………………………….Theoretical % of thread
5/32……………………………………………………..83
22....……………………………………………………..81
21....……………………………………………………..76
20....……………………………………………………..71
19....…………………………………………………….59

For roll form threads 10-32
#16


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## P. Waller (Jul 5, 2018)

If the drawing has a thread class call out such as 10-32 3B stick with the Maximum Minor Dia. allowed by the ANSI standards, if a 2B use the MMD for this thread which will be larger and easier to tap.
Above all do not use hardware store taps, a far more expensive tap will last longer and tap with less force and chance of leaving it in the part.

This is a decent resource that I use when to lazy to go through 60 pages of MH thread data charts, just enter the thread diameter, lead and the class and it will tell you the max. minor diameter and use that for the hole size. If the customer is going to  gauge it all bets are off, it takes very little error for a 3B NG gauge to go in the hole and fail inspection.

If you are just putting parts on your motorcycle/bicycle/BBQ grill use the 2B thread data.

https://www.amesweb.info/Screws/AsmeUnifiedInchScrewThread.aspx


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## oskar (Jul 5, 2018)

I will give a try to different size drill mentioned, thanks to all

BTW I always use wd40 when tapping / drilling

The tapping is for both through / blind holes

I buy my taps from KBC Tools in Ontario


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## francist (Jul 5, 2018)

I buy from KBC as well, I think their quality is pretty good. At least I'm pleased with them.

-frank


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## WarrenP (Jul 6, 2018)

Tony Wells said:


> 3/16" is approximately the major diameter of a #10 machine screw. A 10-32 tap would barely scratch it, even if it drilled perfectly on size.



Hmm, 1/32nd would make that much a difference?  Sorry for leading you the wrong way.  My mistake.


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## Bi11Hudson (Jul 6, 2018)

As usual for me, a day late and a dollar short*........*  My two cents worth, or is it a nickle now?
First off, a Nr 10 machine screw is 0.190" (060+(.013x10))
              Next, a 3/16" stove bolt is 0.1875" (2-1/2 thou smaller)
Threads for 32TPI are 1/32 (0.03125") less than that to tap.
That yeilds 0.15875 as the optimum drill size. Use the closest larger drill for tapping. I don't have handy a chart, but the closest drill may well be metric. Who knows?
I could lecture on aluminium as being tenaceous, but I won't. I do remember breaking more taps in it than in steel. Panel steel was gauge 11, call it 2mm. Aluminium was 3mm, m/l. In my experience, 10-24 was a much more usable size in aluminium. Hanging electrical components*.......* Of course, troubleshooters usually had some 10-24s in their pockets. Only the electronics guys kept extra 10-32s.
Bill Hudson​


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## Tony Wells (Jul 6, 2018)

32 pitch has a nominal thread depth of 0.0192, and doubling that would yield 0.0384. Nominal major diameter is 0.1900, so in basic dimensions, the minor should be 0.1900 - 0.0384 or 0.1516. Recommended (for 75% engagement IIRC) hole size is 0.1590.


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## Z2V (Jul 6, 2018)

I will go with  #21 as others have said. Always worked for me.


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## ch2co (Jul 6, 2018)

Oskar 
Are you hand tapping, or drillpress or using a tapping device that clutches foreword and reverse as you push or pull the tap. ???
It really sounds to me that you are having a problem with the tap itself and need to get a good quality one (get a few if you really are tapping a lot of holes). I think that I might have broken 4-5 taps in my whole life and I typically tap for 4-40, 8-32 and 10-32 fasteners.  A cheap tap is just that, cheap.  A good quality tap should make a bug difference, but get at least a pair just in case.


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## Tinkertoy1941 (Jul 6, 2018)

Tap Charts are not a necessity The Henry Ford Trade school taught us how to use a calculator!
The Formula is divide 1 by the pitch minus the major thread diameter and use the answer to find the hole size
Always go up to the next nearest size drill
3/8" minus 1/16 = 5/16           5/16 is the drill size 3/8 16 tap
this will work for all size taps


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## brino (Jul 6, 2018)

@oskar,

Little Machine Shop has a nice thread chart here:
https://littlemachineshop.com/Reference/tapdrill.php

What I like about that one is that it has columns for 75% thread and 50% threads, so you can choose what works best for your project and materials.
(also note the link on that page for a "printable version" of the table. I laminated it and hung it in the shop.)

-brino


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## pacifica (Jul 6, 2018)

with all this info you should be doing perfect threads!


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## oskar (Jul 6, 2018)

I hand tap guys and its the most boring job but it has to be done

I buy taps in the middle of the price range and in the last 10 years I only broke 2 taps for M5 bolts.


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## umahunter (Jul 14, 2018)

If you haven't yet  try tap magic it works great


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## Kernbigo (Jul 15, 2018)

use a x-press tap that was patented by Besley, also call a expander tap. It was first used on soft metal, now they use on everything, it doesn't cut it expands the metal
I can see this post went over everyones head more than likely no one herd of x-press taps, no metal removal it expands and makes a stronger hole.


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## projectnut (Jul 15, 2018)

As mentioned a #21 drill will give you slightly more clearance.  I would recommend good quality HSS gun taps when threading through holes.  The gun tap pushes the chips forward and through the hole.  When doing blind holes I would start with a plug tap and finish with a bottoming tap.  Be careful to remove the tap and clean out chips regularly when doing blind holes.  Also when using hand taps make sure to reverse direction every 1/4 turn or so.  This breaks the chips and allows them fall into the relieved area between cutting edges.  If you attempt to turn more than 1/2 a turn without reversing in gummy metals the cutting edges will get clogged with chips.

The only time I would consider anything other than a high quality HSS tap is for a one off job.  Carbon steel taps don't last long and break easily when they get dull.  I did buy a carbon steel 9/16-18 left hand tap for what I thought would be a one off job.  Low and behold I've done the "one off job" a dozen more times.  I think it's time to invest in some HSS ones before I hear the dreaded "crack" which, if it happens, I'm sure would be followed by a string of colorful 4 letter words


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## Richard White (richardsrelics) (Jul 16, 2018)

See I don't even bother with the chart too often as my drill index has this handy dandy chart for tap drill size ranging from 2-56 tpi thru 1-8 tpi
It also gives recommended body drill or clearance hole sizes.  After you have done this for 30+ years, some of those numbers just stick in yer head, like #7 for 1/4-20 or in a pinch you can use 13/64 .... boggles my mind just how much of this stuff I personally take for granted because I have done it and used the info for so long...I have always wondered about the % thread stuff... class of fit has a purpose but for most home shops, I cant see that ever being something to worry about.


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## pacifica (Jul 16, 2018)

Kernbigo said:


> use a x-press tap that was patented by Besley, also call a expander tap. It was first used on soft metal, now they use on everything, it doesn't cut it expands the metal
> I can see this post went over everyones head more than likely no one herd of x-press taps, no metal removal it expands and makes a stronger hole.


Probably because you used a proprietary name; aren't they  called thread forming taps and  made by a number of companies, all with a different name: such as tru-ledge(kennametal), Pt 170 taps by precision twist drill, Hy-pro NRT by OSG tap and die, and so on?


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## Silverbullet (Jul 17, 2018)

If your doing lots of tapping , why not invest in a tapping head? Used there pretty reasonable. I've used them and have done literally thousands of holes in aluminium . I even used one on a hand drill that worked super.


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