Practical Screw Thread Information & Tolerances

G

Gordon Clarke

#1
I need some help J

I’d like to start a new forum or “thread”, but how do I go about it? I know this isn't the correct forum or thread, but there doesn't seem to be anything entitled "Start a new thread" :cool:

I’m thinking of a title like:

Practical Screw Thread Information & Tolerances

for people to exchange information on all types of screw threads.

Here’s an example of the kind of thing I’d intend putting in it (and I have much more on other thread types):


Important:
These table are made as a guideline for calculating nominal pitch diameter and pitch diameter tolerances. As the primary purpose is to measure with a digital caliper, most dimensions are calculated to the nearest 0.01 mm.
When a tolerance in a table is used, it should be remembered that the tolerance will often be slightly larger for a finer pitch than standard. i.e. the pitch diameter tolerance for M60x2 is larger than for M36x2, which again is larger than that for M16x2 – which is standard.
For exact tolerances use the relevant, approved standard.


Pitch diameter tolerances
Thread
Nut (6H)​
Bolt (6g)
M16x2

M36x2
M60x2
M120x2
+0.212 / -0
+0.224 / -0
+0.236 / -0
+0.250 / -0
-0.038 / -0.198 (0.16)
-0.038 / -0.208 (0.17)
-0.038 / -0.218 (0.18)
-0.038 / -0.228 (0.19)


Nominal Pitch diameter = Nominal Major diameter
- (minus) PDN
I.e. Nominal Pitch diameter for :
M20 x2 = 20.00 - 1.30 = 18.70
and 1-8UNC = 25.4 - 2.06 = 23.34

ISO METRIC - 60O
Pitch diameter tolerances

Pitch
PDN
Nut (6H)
Bolt (6g)
1
1.25
1.5
1.75

2
2.5
3

3.5
4
4.5
5

5.5
6
0.65
0.81
0.97
1.14

1.30
1.62
1.95

2.27
2.60
2.92
3.25

3.57
3.90
+ 0.15 / - 0
+ 0.16 / - 0
+ 0.18 / - 0
+ 0.20 / - 0

+ 0.21 / - 0
+ 0.22 / - 0
+ 0.26 / - 0

+ 0.28 / - 0
+ 0.30 / - 0
+ 0.31 / - 0
+ 0.33 / - 0

+ 0.35 / - 0
+ 0.37 / - 0
- 0.03 / - 0.14
- 0.03 / - 0.15
- 0.03 / - 0.16
- 0.03 / - 0.18

- 0.04 / - 0.20
- 0.04 / - 0.21
- 0.05 / - 0.25

- 0.05 / - 0.26
- 0.06 / - 0.28
- 0.06 / - 0.30
- 0.07 / - 0.32

- 0.07 / - 0.34
- 0.08 / - 0.36


UN (ISO Inch) - 60O
Pitch diameter tolerances

Pitch

PDN
Nut (2B)
Bolt (2A)
24
20
18
16
14

13
12
11
10
9

8
7
6
5

4
0.69
0.825
0.92
1.03
1.18

1.27
1.37
1.50
1.65
1.83

2.06
2.36
2.75
3.30
3.665
4.125
+ 0.11 / - 0
+ 0.12 / - 0
+ 0.14 / - 0
+ 0.15 / - 0
+ 0.16 / - 0

+ 0.17 / - 0
+ 0.17 / - 0
+ 0.18 / - 0
+ 0.20 / - 0
+ 0.21 / - 0

+ 0.22 / - 0
+ 0.24 / - 0
+ 0.26 / - 0
+ 0.30 / - 0
+ 0.32 / - 0
+ 0.34 / - 0
-0.025 /- 0.11
- 0.03 / - 0.12
- 0.03 / - 0.13
- 0.03 / - 0.15
- 0.04 / - 0.16

- 0.04 / - 0.17
- 0.04 / - 0.17
- 0.04 / - 0.18
- 0.05 / - 0.20
- 0.05 / - 0.21

- 0.05 / - 0.22
- 0.06 / - 0.24
- 0.06 / - 0.26
- 0.07 / - 0.30
- 0.07 / - 0.32
- 0.08 / - 0.34



Living in Europe I normally work with mm but I also have the same tables in inches.

I sometimes find myself needing information too :agree:

Thanks,

Gordon
 
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harry

Super Moderator
#2
Re: Screw Thread Information

Welcome,

You had already started a thread. I had just moved it to the appropriate forum: ISO 17025 - Calibration and Test Laboratories, Measurement and Gages. This is where all discussions on this subject take place.

Please carry on.


Added in edit: I will delete your latest post on starting this thread in the other thread: New Folks - Please Take a Minute and Introduce Yourself/Say Hello!
 

Wes Bucey

Quite Involved in Discussions
#3
Just a reminder - when the layout of a chart or graph (or even the typography) seem important, consider adding an attachment (scroll down when making a post to the section
Attach Files Valid file extensions: bmp doc dot dwg dxf flv fp5 gif gz jpe jpeg jpg mdb mov mp3 mpp pdf php png pps ppt psd rar sdr tar tgz txt vsd xls zip

Manage Attachments
When you are unsure of how others may be able to view or open a file, it is often efficient to convert the document to a pdf file and attach the pdf file. Free utilities are available on the internet for making such conversions.

We cover this and a lot more in threads contained in the Forum Instructions --> How To Use the Forum Software
 

harry

Super Moderator
#4
May I also add that at any time when you feel that you need the help of a moderator - whether to move a thread or post, to rename or retitled a thread or if you are facing technical difficulties, use the 'Report this Post'
button in RED (triangle)
and at the top right hand corner just next to the 'Karma" button.

A report will be generated immediately and any moderator who are on-line will respond to you. This is the fastest way to get help.
 

Wayne

Gage Crib Worldwide
#5
...These table are made as a guideline for calculating nominal pitch diameter and pitch diameter tolerances. ...For exact tolerances use the relevant, approved standard....
So the numbers calculated by using this table are not the actual values which would be listed in the relevant standard?
If these are not the accurate numbers, why use them?
Why not just use the relevant standard?
 

Stijloor

Staff member
Super Moderator
#6
So the numbers calculated by using this table are not the actual values which would be listed in the relevant standard?
If these are not the accurate numbers, why use them?
Why not just use the relevant standard?
Excellent questions Wayne! I hope Gordon will respond.

I remember from my machinist's days that we had some quick reference tables to find tap drill sizes.
We also used some other screw thread-related manufacturing "trickery" that evolved over the many years, but did not necessarily "violate" standard requirements.

Stijloor.
 
G

Gordon Clarke

#7
Hello Wayne and Stijloor (Dutch origin?)

Thanks for the comment(s) and it shows that there is interest :)
However there is a relevant answer. I'm going to refer to mm and not inches as they are almost never used in Europe, so if anyone isn't too familiar with the metric system just divide mm by 25.4 to arrive at inches.

In the relevant tables I use (usually ISO standards), dimensions and tolerances for screw and nut tolerances are given to within 0.001 mm (0.00004 ins.) The standard pitch diameter tolerance for a M6-6g screw thread thread is (for example) 0.112 mm and for a M6-6H nut is 0.150 mm. I'd round the screw tolerance down to 0.11 but the nut is OK as it is 0.15.

In the real world, only someone with too much time on their hands (written with a smile) would measure a tolerance of 0.1 mm or more, in 0.001 mm.

I know many that measure a thread using a 0.01 mm caliper and thread wires. When the constant for thread wires is subtracted the result is usually a "measurement" to within 0.001 mm. I'd round up or down unless the result ended in 0.005 mm. If a thread was to be measured in 0.001 mm I think I'd want to know the exact flank angle and pitch too.

This is why I've given my tables to the nearest 0.01 mm. My tables are only meant for component measurement and not for gauge measurement.

I explain all this in detail in my tables (and refer to the standard used), and that's why it is important that I include the tables as a document and not a "reply". I'm still figuring out how to attach a document as I have made many of them for many thread types.

I hope this explains my motivation, because of course I use the relevant standard values - just not to within 0.001 mm. This would defeat the purpose of my measurement methods and tables, by giving people the opinion (or impression) that thread pitch diameter measurement neded to be measured within 0.001 mm - it certainly doesn't.

In a "Calibration" related thread, I'm probably with people who work in temperature controlled environments - my target "audience" is machinists and production technicians in general who measure machine produced components.

Is my explanation OK and (almost) acceptable?

I'll include my tables a.s.a.p. - I promise!

Gordon

P.S. My reasoning and logic should be even clearer if you look at my website.
There's method and logic behind my madness. :) - at least I hope so.

P.P.S. I can't resist this:
What's the difference between the Scots and the English?
The English are the ones with the nice neighbours!
 
G

Gordon Clarke

#9
Harry (and anyone else)
Thanks and I'm sure I'll figure it out. I'm a bit pushed for time at present but I'll get there when I've studied the instructions carefully :)
Gordon
 
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