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Re: Standard Gages

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> From: "Lutz, James" <JLUTZ(--nospam--at)>

> A colleague just asked me a question for which I had no answer. Is there any
> sort of officially adopted US reference standard that defines gage thickness
> for sheet metal? There is a table in the back of the AISC steel manual that

> From: Christopher Wright <chrisw(--nospam--at)>

> The gage numbers originally denoted the weight of material based on an
> assumed weight of 41.82 lb/sq ft per inch of thickness. That's a density
> of 0.29042 lb/in^3 (which isn't actually the density of steel). 

> thickness is 0.0359 in. The thicknesses in handbooks are derived numbers
> and they'll vary depending on the density used to go from weight to 
> thickness. You can see how the confusion got started. Best practice is to
> order by thickness.

Aha, one of my pet peeve topics. Sheet steel gage is as fuzzy as the
marketing guys want to allow and as misunderstood as the best
advertising can make it. I have not met a person who has written a sales
brochure who understands what they have written and many project spec
writers could do better. Refering to gage thickness is like calling a
colour BLUE without considering the many variations in hues.

Christopher is correct on all points in reference to the "Manufacturer's
Standard Gage" as opposed to one of the several other "gage" measures.
It has no useful engineering purpose and was never an offical measure
for commerce (coils are ordered by thickness but sold by weight!). There
is no organization that maintains it and its use is discouraged at the
mill and primary manufacturer's level. It is still used for convenience
due to end-user ignorance fostered by selling practices (some bordering
on fraud). It is peculiar to North America.

I haven't gotten my hands on a copy, yet, but I believe that the 2002
North American (AISI/CSA/M???) cold-formed design standard establishes
the engineering analysis thickness for sheet to be the actual measured
thickness with a statistical probability that all areas exceed 95%, or
something similarly specific. Measuring procedures are established in
ASTM specs.

> Gage numbers will make you crazy.

They're coming to take me away, haha ....

Paul Ransom, P. Eng.
Burlington, Ontario, Canada
<mailto:ad026(--nospam--at)> <>

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