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Correct Format for Thread Callout

Correct Format for Thread Callout

Correct Format for Thread Callout

I am new to this forum. I have performed a search of Eng-Tips but so far have not found an answer to my exact question as far as I have been able to locate. Please provide a link to the correct post if I overlooked it.

Right now my company does not have access to ANSI/ASME Y14.6 which I think would answer the question. I have submitted a request to the department head to purchase a copy, but I would prefer not to wait for the wheels to grind out a response.

Here is my specific question about the two schools of thought, using a typical thread callout. The difference is one group says also call out diameter of the hole to be drilled to prepare for tapping, second group says don't include diameter of the hole, the thread callout handles it all.

First school of thought:

.138-32 UNJC-3A
{diameter symbol] .1076-.1157

NOTE: We have these diameters published in our engineering design manual, but I have not been able to locate their source. I did not find them in AS8879, the replacement for MIL-S-8879, the former standard for UNJ thread callouts. AS8879 does not show a diameter callout but I still want to get input from ANSI/ASME Y14.6 if I can.

Second school of thought:

Same thing but do not call out diameter.

If someone could provide a quote (or a screen shot of the page) from ANSI/ASME Y14.6 that would be great and would serve me well to help update our drafting manual until the department head gets us our own legitimate copy of the standard.

Thanks in advance for your assistance.

RE: Correct Format for Thread Callout

Typically, 2nd school of thought. The thread size, pitch, and class as well as the type of tap the machinist is going to use determines the proper drill size. Engineering drawings typically do not specify manufacturing methods, that includes tap drill sizes.


RE: Correct Format for Thread Callout


Thank you for the reply. Your point matches all of the research I have completed so far, and will bolster my request to the department head for our own copy of the standard.

RE: Correct Format for Thread Callout

I've written about this before as well:


There are issues with over-specification and wrong-specification. Forming method, material and shop process can all be a factor in determining the drill size. You don't want to tie down your vendor into using a method that is more costly.

Matt Lorono, CSWP
Product Definition Specialist, DS SolidWorks Corp
Personal sites:
Lorono's SolidWorks Resources & SolidWorks Legion

RE: Correct Format for Thread Callout

It comes in part from ASME Y14.5M section 1.4 where it talks about only detailing the finished item - perhaps you do have access to that spec?

The problem with specifying the tap drill is that there is more than once potential tap drill depending on thread forming method, material and other factors.

However, there are times when it is necessary to specify the tap drill dia for some functional reason (such as on a pneumatics manifold where the 'tap' drill continues on to intersect other holes). Y14.6 allows for this at third paragraph and in 3.3.11.

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: Correct Format for Thread Callout

fcsuper: Thanks, I read the entry on your blog and that made it very clear for me.

Kenat: Thanks, and I will review ASME Y14.5 section 1.4 for further information since we do have access to that document. I have made the request of our department head for a copy of ASME Y14.6 but he is on vacation so I don't know yet if he will or won't agree. If we do obtain it, I will definitely pay attention to the two sections you noted as well as completing a review of the entire document. It was listed as $44 on the website so I hope he will approve since the cost is so low.

RE: Correct Format for Thread Callout

There ARE times when you will want to specify the drill diameter. In those instances, including the drill diameter is appropriate; otherwise, no.

Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com

RE: Correct Format for Thread Callout

I know that modified (for whatever reason) threads may include the minor diameter in the callout, or when the minor diameter continues beyond the thread as noted above, but are there other situations where it is desireable to do so?

“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV

RE: Correct Format for Thread Callout

Our deigners use the decimal equivelant on all thread callouts; <dia_sym>.500-13 UNC-2B.

"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

RE: Correct Format for Thread Callout

My suggestion is callout what the tap/die indicates. Why use something non standard to make more work for the machinists? The more confusion, the more errors.

SolidWorks 11
ctopher's home
SolidWorks Legion

RE: Correct Format for Thread Callout

the best example that I can think of is with "specialized" threads such as Spiralok. They are very particular about the predrill sizes in their specs (as I recall), and when I've worked with them, our manufacturing engineers had to play with the predrill sizes a bit to get a good combination of tapping speed and thread locking performance. In that case, we had to specify on the drawing what we wanted because otherwise the machinist or supplier would go with a normal predrill size without knowing the difference. It made a critical difference on functionality.
I've also seen a few cases where someone changed the predrill size so that the hole could be used more acurately to locate a hidden component during the assembly process; not a normal application, but valid and useful nonetheless.

I have seen decimal inches used for numbered bit sizes a few times; it had to do with a comprehension problem in Europe. They didn't have references for the numberd and lettered bits.

Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com

RE: Correct Format for Thread Callout

ctopher, per the standard the way debodine has it using decimal diameter is actually the preferred way. It says "Numbered sizes may be shown because of established practices. The decimal equivalent, to three decimal places, should be shown in parenthesis."

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: Correct Format for Thread Callout

My thoughts have always been, never let the machinist make any decisions. A drawing should have all the information to machine the part.

Drill (8) 1.00 DIA x 1.625 MAX DEEP.
TAP 1-1/8"-8UN-2B X 1.12 FULL THREAD.
PITCH DIA: 1.0528-1.0438
MAJOR DIA: 1.1250 MIN.
MINOR DIA: 1.015-0.990 REF.

Petrotrim Services

RE: Correct Format for Thread Callout

There are decisions that machinists make every day that are not spelled out on any print.

To specifically address your note, you didn't say anything about how fast to spin the drill bit. Does that mean I have to make that decision on my own? I suppose I couldn't interpolate the hole either since you specifically want it drilled for some reason.

Do I tap with a cutting tap or a forming tap? A forming tap would probably break off in the hole but apparently that's not a decision I'm capable of making. Thread milling this hole would be easy, but since I don't have a 1-1/8-8 tap I'll just buy one and charge you for it.

I'm glad to see that you made a great decision on what the pitch diameter, major diameter, and minor diameter should be. They all line up perfectly with what's in the machinists handbook. You're definitely one smart dude.

As far as the part that the hole is drilled in goes; will I have all the information I need spelled out for me? Things like cutter material and size, feed rates, spindle speeds, holding methods, depth of cuts--both radially and axially--are important decisions that I will need you to make for me.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

RE: Correct Format for Thread Callout


That gave me a good laugh. Its clear your the best of the best, since you post "titles" under your name, you must be one smart dude. I see you do not understand a machinist role in the company. At no point should a machinist make an engineering decision, hole size, included. I suppose if engineering wanted the hole drilled 0.875 instead of 1.00, you would make the necessary changes since you understand the intend of the design far better than engineering.

From your past post "If a machine shop gets a print with no GD&T on it as well as no reference to any dimensioning standard, how much responsibility does a machine shop have to catch any unspecified tolerances" I thought you didn't need any guidance, why would a print need that information, if your a first class machinist?

Your a smart guy, have I made any other posts in the GD&T forum? Sorry for stepping in your house since you seem to run the place with your 250 plus posts. I don't come hear to ask questions on how to do my job, I answer questions and provide information from 23 years of experience, from being a machinist and engineer.

Petrotrim Services

RE: Correct Format for Thread Callout

I suppose you've worked with subpar machinists because my experience has shown it is best to specify the end-result rather than go into process specifics. To start specifying HOW a machinist makes something is a recipe for cluttered drawings, mistakes, and higher costs. For the most part machinists are highly-skilled and are used to making decisions on their own about HOW to get there. A fundamental property of engineering drawings is that they focus on WHAT needs to be made not HOW to do it. That's what work instructions are for.


RE: Correct Format for Thread Callout


Allow me to present another way. If engineering does not provide a drill size, manufacturing provides the drill size, drill size is in correct, scraps 1000 parts. Who would receive the blame? Engineering for not providing all the information needed to correctly drill and tap the part, or manufacturing.

I am not dogging machinists, they are highly skilled, I have over 40 machinist working for me, running horizontal milling centers, to small lathes.

Petrotrim Services

RE: Correct Format for Thread Callout

Not to mention Gaging standards. 40 machinists who cannot tell good thread from bad thread and have to be baby-sitted.


RE: Correct Format for Thread Callout

Jbeckhou -- I don't know if it's been mentioned above as to what standard your drawings are using (and there should indeed be a note imposing a standard) but the ASME standard Y14.5 clearly states in paragraph 1.4(e) that "the drawing should define a part without specifying manufacturing methods."

So engineering merely needs to tell the machinist what the finished part should look like. You say that if they choose the wrong drill and create bad parts that it is the engineers who get blamed? Perhaps they get the blame from those who don't know the governing rules, but the standard exonerates the engineers in that case.

Engineering really doesn't care how the part is made. What if I toss the part up in the air and shoot a hole through it with a gun? Hey, as long as the hole ends up meeting the drawing requirements, it's a good part.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

RE: Correct Format for Thread Callout

JP, is that "gun drilling"? wink

“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV

RE: Correct Format for Thread Callout


How many holes have you drilled and tapped?

I figure I have done around thirty in my lifetime. That, probably, is more than many other people in this forum. Thirty tapped holes do not qualify me to argue with machinists. They are supposed to know what they are doing.


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