Thread specification on German drawing 4

[minerk]

I've got a German drawing produced in the early '80s that specifies a few threaded holes as: M24 "b". Does the "b" indicate pitch? And if so, what pitch?

Thanks in advance,

minerk

 

[insideman]

In America a and b refer to male and female threads respectively. I suspect the same is true in Germany.

 

[Heckler]

A good example of metric thread callouts can be found in the Machinery's HDBK:

M24x2-4g6g EXT

M24x3-6H INT

According to the MH it's a simplified international practice for designating coarse pitch M profile metric screw threads is to leave off the pitch. Thus a M24x2 thread is designated just as M24.

Heckler
Sr. Mechanical Engineer
SWx 2007 SP 4.0 & Pro/E 2001
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_`\(,_
(_)/ (_)

"Avoid the base hypocrisy of condemning in one man what you pass over in silence when committed by another." -- Theodore Roosevelt

 

[minerk]

Thanks Heckler! A star for you. I had looked in MH but missed that. Checked again after your post and found it.

 

[KENAT]

Not sure what the b would mean. I don't recal using it on Metric threads in the UK for male/female but may have been different back then in Germany.

US is the only place I know of where you don't just leave off the pitch to specify standard course pitch.

KENAT, probably the least qualified checker you'll ever meet...

 

[CorBlimeyLimey]

I've never heard of a and b being used to designate male and female threads ... anywhere.

 

[KENAT]

CBL, you've obviously never specified UN series threads, or at least specified them correctly to ASME B1.1;-).

Unless you were making the point it should be A & B.

I thought b may be something to do with DIN ISO 2768-1 but they only appear to use f, m, c, v, H, K & L and I'm not sure it would apply to a thread anyway.

"US is the only place I know of where you don't just leave off the pitch to specify standard course pitch. " - this only applies to metric threads, should have been clearer.

KENAT, probably the least qualified checker you'll ever meet...

 

[mrainey]

It's my understanding that the case of the tolerance position defines whether an ISO thread is male or female.

external = e, f, g, or h
internal = G or H

M6-6h is male
M6-6H is female


Software For Metalworking

http://mrainey.freeservers.com

 

[CorBlimeyLimey]

KENAT ... I'm confused by your statements.
In your first post, "Not sure what the b would mean"
So obviously you were not familiar with the a/b = male/female thread designator either.

In your second post, "CBL, you've obviously never specified UN series threads, or at least specified them correctly to ASME B1.1 "
Does ASME use the a/b designation for male/female threads? If so please post an image of how it should be shown.

Also in the second post, "I thought b may be something to do with DIN ISO 2768-1 but they only appear to use f, m, c, v, H, K & L and I'm not sure it would apply to a thread anyway"
Back to first post.

 

[dimjim]

For inch series,
it is quite common to specify external
threads by adding 1A or 2A or 3a
and internal threads by adding
1B or 2B or 3B for the inch series.

For example 3/4-10UNC-2B

This indicates the tolerance field by the
external or internal thread.

For metric threads i.e.
M24-4g6g lower case indicates external
no pitch designated coarse thread

M24x3-6H upper case indicates internal

I have never seen "b" as a designation for
a tolerance field but if it is specified
to a particular din standard it may indicate
per that din standard an "a" "b"
designation as in tapered, straight
for a grease type thread din standard.

Or is it simply defining a footnote on
the drawing?

 

[CorBlimeyLimey]

KENAT ... Please ignore my last post. I overlooked the second line of your second post. I now understand what you meant regarding the UN threads.

 

[KENAT]

No problem CBL, it probably wasn't as humorous in writing as in my head.

KENAT, probably the least qualified checker you'll ever meet...

 

[JCJackson]

The 'b' could refer to a note controling the execution of certain holes; e.g. "HOLES MARKED 'b' TO BE EQUALLY SPACED"

 

[Cockroach]

Naw, I totally agree with DimJim.

A=external or pin, B=internal or box threads, in the imperial system either class 1, 2, or 3. I use this convention all over my prints for the past forty (40) years.

His example "3/4 - 10 UNC-2B" is bang on!

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[minerk]

There is no footnote on the drawing that the 'b' refers to. The holes in question are in a flat plate, so I don't see why there would be a need to specify internal or external threads.

After reading Heckler's response I found the page in MH that he refers to, and am treating the thread as coarse pitch.

Thanks for all the input!

 

[Timelord]

minerk,

cockroach is correct, the 2B refers to the tolerance class and the B indicates internal threads. The B is a not there to specify the thread, but as a modifier of the tolerance class. Internal and external tolerances are different for the same class, so it is a part of the tolerance callout.

Timelord

 

[minerk]

I'd agree if we were discussing UN series threads. However, if you refer to my original post, the drawing indicates 'M24 "b"', not "3/4 - 10 UNC-2B". I have not found a DIN (these are German drawings) or ISO standard that includes a "b" tolerance class, or uses "b" as an indicator of internal or external thread.

 

[Cockroach]

It's very hard to say, Minerk. Probably seeing the entire drawing and looking at the big picture would be helpful.

But good luck with it none-the-less.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[JCJackson]

I have consulted a German engineering associate on this and I quote his answer verbatim:

"We don't have an ensured explanation for the "b".
M24 is for sure a metric thread
We have used in the '80s such a "b" as an exchange index on drawings. Example: if the tread was before M20 and we changed it to M24, the whole drawing remains with the same number, but Index "b"."

Check the revisions block. I can't do any better than that.

 

[KENAT]

That may make sense, it could be a rev change indicator, showing what changed from rev A to B.

KENAT, probably the least qualified checker you'll ever meet...