.7500-28 UNJEF-2B ??? 1

[mrainey]

I've been asked by a colleague to furnish specifications for a .7500-28 UNJEF-2B thread, which he says is called out on a customer-furnished drawing.

All the internal J-series threads I've ever read about have been class 3B. Furthermore, I don't see .7500-28 UNJEF listed in any reference.

Does anybody have any information which could help me determine if this thread actually exists?

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[israelkk]

MIL-S-8879 at

http://assist.daps.dla.mil/quicksearch/

. Search for this document in the "Documnet ID" zone.

 

[israelkk]

By the 0.75-20 UNJEF is the extra fine and not 0.75-28 UNJEF according to MIL-S-8879C table IV page 21. I suspect it is a typo error in your drawing or a special thread. If it is a special thread and if I am not mistaken in should be 0.75-28 UNJS-2B. You are correct, all UNJ threads are class 3A or 3B.

 

[mrainey]

Thanks very much. Your information supports my suspicion that the callout is incorrect. I'll send a copy of your answers to the man with the question.

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[Kenneth]

The 0.7500-28 UNJEF designation does feel like a typo. As noted by israelkk above the "EF" designation for this diameter is for a 20 TPI thread, and if the intent is really to call out a "Special" 28 threads-per-inch thread for this diameter, a "UNJS" (and not "UNJEF") designation would be expected.

However, while it is true that all MIL-S-8879 (now AS8879) UNJ threads are Class 3, not all "UNJ" threads are Class 3. ASME B1.15 (

http://members.asme.org/catalog/ItemView.cfm?ItemNumber=N13195)

tabulates dimensions for Class 2 UNJ threads.

 

[mrainey]

Thanks Kenneth,

I wish I could read the standard you reference, but fifty bucks for a 72 page document is more than I can justify.

In twenty five years of working with blueprints from many different companies, both in and out of aerospace, I've never run across a class 2 UNJ thread.

You can learn something new every day.

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