×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Fractional vs Decimal Screw Thread Callout

Fractional vs Decimal Screw Thread Callout

Fractional vs Decimal Screw Thread Callout

(OP)
Interestingly enough, one of our draftsmen recently put together a print that had fractional screw thread dimensions (ex. 1/4-20 UNC-2B). I didn't think much of it until our customer questioned the callout. I often see threads called out with decimals, but do any of the ASME standards give guidance on which is more appropriate?

RE: Fractional vs Decimal Screw Thread Callout

Quote (ASME B1.1-2003 section 6.):

  "...The nominal size is the basic major diameter and is specified as the fractional diameter, screw number, or their decimal equivalent.  Where decimal equivalents are used for size callout, they shall be shown in foru place decimals (omitting the cipher in the fourth place) for fractional sizes, and in three place decimals for number sizes. ..."

So one might argue fractional is slightly preffered in that standards.

In ASME Y14.6-2001 Screw Thread Representation says similar, though if using number sizes it says you should add the decimal in parenthesis, which isn't quite what B1.1 says.

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: Fractional vs Decimal Screw Thread Callout

(OP)
Well, I guess that answers it. I found the paragraph that you're referring to. What do you suppose that they mean by:

Quote (ASME B1.1-2003):

Where decimal equivalents are used for size callout, they shall be shown in four place decimals (omitting the cipher in the fourth place) for fractional sizes, and in three place decimals for number sizes.

I've always invoked number sizes as "6-32 UNC-2B". Are they recommending "6.000-32 UNC-2B"?

RE: Fractional vs Decimal Screw Thread Callout

No.  They mean ".138-32 UNC-2B".

.138 is the decimal equivalent of #6.

Actually, in B1.1 they appear to use leading 0's which is odd for an inch standard.

Per 14.6 it would actually be "No. 6 (.138)-32 UNC-2B" or 6 (.138)-32 UNC-2B".

As I've mentioned before the 2 specs don't quite match on some details.

What you put would I believe be a 6" thread.

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: Fractional vs Decimal Screw Thread Callout

(OP)
6" Extra, extra, extra, extra fine. wink

It sounded a bit odd when I read it yesterday, but now that I've reread it, it's clear what they're talking about.

RE: Fractional vs Decimal Screw Thread Callout

RE: Fractional vs Decimal Screw Thread Callout

I think there was a battle about this in the past and the fractionists kinda won for the decimalians. :)  For my money, fractions are harder to read when designing, but easier to interpret because they don't accidentally invoke standard decimal place drawing tolerances.

Matt Lorono
Lorono's SolidWorks Resources & SolidWorks Legion

&

RE: Fractional vs Decimal Screw Thread Callout

I also think this has been addressed before, but I don't remember giving in. winky smile

"Good to know you got shoes to wear when you find the floor." - Robert Hunter
 

RE: Fractional vs Decimal Screw Thread Callout

You can't go wrong specifying the decimal size.  It would be awfully hard to incorrectly transcribe .250-20 UNC-2B.

Tunalover

RE: Fractional vs Decimal Screw Thread Callout

Quote (fcsuper):

I think there was a battle about this in the past and the fractionists kinda won for the decimalians. :)  For my money, fractions are harder to read when designing, but easier to interpret because they don't accidentally invoke standard decimal place drawing tolerances.  

   The 2B specification as per Tunalover's post above, supersedes the tolerance block.  Most English tolerance blocks don't define four decimal places, anyway.

   I prefer the number (6-32UNC-2B) and fraction (1/4-20UNC-2B) myself because usually, that is what is written on the taps and on the inspection gauges.    

               JHG

RE: Fractional vs Decimal Screw Thread Callout

We use the fractions in callouts on drawings.  But for hardware descriptions in our PLM, we use decimal for 1/4 and above, and the ## for 0-12.  Sorting is not perfect this way, but still better than if we used fractions.

Matt Lorono
Lorono's SolidWorks Resources & SolidWorks Legion

&

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources