Question About Threads 1

[dmorong1]

Hello,

Please see the attached file. The drawing calls for a 5"-12 UNC-2B threaded thru hole. Is this a legit thread callout? I've found one mention of it in my machinery's handbook in the "Recommended Hole Size Limits Before Tapping Unified Threads" table but am struggling to find any more information about this type of thread in any thread charts, etc. Any nudge in the right direction would be appreciated.

 

[ornerynorsk]

While it's debatable whether 5"-12 would be UN, UNC, or UNS, it is for the most part a legitimate callout. You may have to extrapolate the tolerance limits for the class 2. It is generally a better practice to have this data called out in black and white on the drawing when there is a possibility for ambiguity. Not sure what the more modern Machinery's has, but my 21st edition only charts complete data up to 4 inch.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[hydtools]

Does this help?

https://www.gewinde-normen.de/en/12-un-thread.html

Ted

 

[ornerynorsk]

Here again, you may have to extrapolate your data. The chart from the German website has no useful information to a machinist. "B" indicates an internal thread, for which you need a minor diameter range, both upper and lower limit, and a pitch diameter range, both upper and lower limit.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[dmorong1]

Thank you all for the help! In addition to what you have all posted I was also able to find 12-thread series basic dimensions in table 3g in the Screw Thread Systems section of my Machinery's Handbook (seventeenth edition).

 

[hydtools]

Thank you for the feedback.

Ted

 

[pylfrm]

dmorong1,

ASME B1.1 is the official reference for this.

UNC, UNF, and UNEF are not defined for diameters this large. The proper designation is 5–12 UN-2B or 5.000–12 UN-2B.

Tolerances (in inches) are as follows:

Minor diameter: 4.910 - 4.928
Pitch diameter: 4.9459 - 4.9546
Major diameter: 5.0000 - 5.0207


pylfrm