Multi anvil thread micrometer-& pitch diameter specs.??

[Janderso]

I am trying to dial in my understanding and use of the Shars 0-1” multi anvil thread mic set.
I installed the two anvils for 13 tpi. I zeroed the anvil as directed.
I’m measuring 1/2” x 13tpi from a store bought grade 5 bolt.
I am getting .444” pitch diameter.

Here is where it gets confusing. I’m referencing the, Engineers black book”, and the 12th and the 19th edition of the Machinery’s Handbook.
The black book shows the minor diameter of (78). I assume that’s .078” less then the major diameter of .500”?? =.422”

The 19th edition for a 2A thread shows the minor pitch diameter of .4435” (I measured .444”) so I agree with this spec.

The 12th edition shows major pitch diameter of .4501”.

If I were to look up the pitch diameter from the three examples, make the bolt and send it off to a customer in some far away land, I wouldn’t have a happy customer.

What gives here? Why so many inconsistencies in the specs from known good sources?

 

[benmychree]

Perhaps it depends on the class (fit) of the particular thread, there should be columns of figures for each thread class.

 

[Asm109]

Its right there in your third picture. Class 2A max pitch diameter .4485 minimum pitch diameter .4435 .
You measured .4440 That is within spec.

 

[Asm109]

What are the details on the table where the OD is .5 inches and it provides a nominal pitch diameter for EVERY TPI.
Which thread standard? That table cannot be a Unified thread standard because a lot of those are not even special threads.

The first table with the 78 , I have ZERO idea what they are trying to convey, for that reason alone I would chuck that in the trash. If they can't label a column coherently, I don't trust or use it.

 

[WobblyHand]

Table 4, Unified Screw Threads, in my 17th ed Machinery's Handbook is the same as post #3

External 1/2-13 UNC Class 2A
max PD 0.4485"
min PD 0.4435"

External 1/2-13 UNC Class 3A
max PD 0.4500"
min PD 0.4463"

 

[Janderso]

You guys seem to be ok with the specs.
Maybe I just need to make sure I’m comparing apples to apples in the same thread class.
It just seems confusing as hell to me.
Yeah, the black book has had me wondering about that column for some time.

 

[mmcmdl]

All threads have limits . They depend on class as Bemmy said . When machining , shoot for nominal of the two limits .