On Fri, 24 Oct 2008 01:28:41 -0500, Richard J Kinch
wrote:

Ned Simmons writes:

I don't doubt that's what you meant, but not what you said,
specifically, "To cut real standard threads, you must stay within
allowances..." The allowances are single values, not ranges that "you
must stay within." That's a better description of tolerances.

Yes, an allowance proper is a single value, not a range. But it is a
single value within which you must stay, an upper or lower limit or worst
or best fit, the tolerance being the specification for how much within.
The allowance informally is what I've called that shaded area in MH 16 p
1762 fig 6, because that is where the thread surface is "allowed to be".
But I suppose the term "limits" would be more appropriate, although this is
not a term in the standards.

"Limits" makes sense to me.


It may seem like quibbling, but your use would
likely confuse the concept of allowances vs. tolerances for someone
who hasn't read those pages carefully.

Confusing things is a specialty of mine. I've read those pages carefully
and am still somewhat confused. But at least now my parts don't come back
with "won't fit" complaints.

I certainly don't claim to understand the whole subject either. For
instance, the thread tables aren't sufficient to completely specify a
good thread. It seems at least one more toleranced dimension is
required. I suspect the key is the illustration in my MH that shows
the proportions of internal and external thread at maximum material
condition, but I've never had a good enough reason to take the time to
work through it.

--
Ned Simmons