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
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.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Fractional vs Decimal Screw Thread Callout
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
.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.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Fractional vs Decimal Screw Thread Callout
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
More links:
ht
http://mdmetric.com/tech/tict.htm
http://ww
http://www.carrlane.com/TrigBook/TrigBook1.cfm
http://www.wikihow.com/Read-a-Screw-Thread-Callout
Chris
SolidWorks 09 SP4.1
ctopher's home
SolidWorks Legion
RE: Fractional vs Decimal Screw Thread Callout
Matt Lorono
Lorono's SolidWorks Resources & SolidWorks Legion
&
RE: Fractional vs Decimal Screw Thread Callout
"Good to know you got shoes to wear when you find the floor." - Robert Hunter
RE: Fractional vs Decimal Screw Thread Callout
Tunalover
RE: Fractional vs Decimal Screw Thread Callout
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.
RE: Fractional vs Decimal Screw Thread Callout
Matt Lorono
Lorono's SolidWorks Resources & SolidWorks Legion
&