Thread No-Go plug gage allows 3 turns to enter. That's too many!

[DTM]

After over 25 years of engineering, designing and analyzing bolted joints, I just learned this little fact. According to ASME B1.2, Gages and Gaging for Unified Inch Screw Threads:
"The no-go gage should not pass over more than three complete turns when inserted into the internal thread of the product. "

3 turns seems like way to much. I have some really critical nuts that are of standard geometry (5/8"-11 UNC 3B) and have about 4.5 threads when you account for the chamfers on either end. So this is saying that 2/3 of my threads could be drilled out to nearly the major diameter, leaving me with only 1/3 the thread engagement I expected, and that's an acceptable nut? That's not how I've been calculating my thread engagement.

We got a batch of nuts that our No-Go plug gages goes in between 2.5 and 3.5 turns on different pieces. It's totally loose for the first couple of turns. The fastener vendor is saying this is acceptable and according to ASME B1.2, for at least the ones with less than 3 turns, he may be right.

I'm I going to have to put notes on all my prints calling out no more than 1.5 turns of a no-go plug gage may enter the part?
Has anyone else dealt with this? Any suggestions of a different spec we should consider calling out?

 

[Lnewqban]

Would this help?:

https://www.thegagestore.com/docs/H...s_and_Accessories-How_to_Use_Thread_Gages.htm

 

[Ranger Mike]

As with all things Government is involved with, confusion.
The Old ANSI standard was 1 1/2 turns. two turns Max. Then the newer standard permitted 3 turn maximum and NO FORCE.
My guess is the manufacturer did not like the high scrap rate caused by 1 1/2 turns.

Read the link below for traditional old style GO NO GO thread plug gages.

https://www.threadcheck.com/how-to-...EednjlJu-VCHoxOETG0leU0mcj6PXnJIMzRN9DFuEI9C_

The go thread plug gage should engage the internal threaded part with very little force used. The engagement should be smooth. There is no specification regarding torque or pounds of pressure for using thread plug gages. Common sense should be applied based on factors of thread size, pitch, and application. If the gage starts to bind, the inspector should stop before damaging the part or the gage. The part may be undersized or tapered. Other possibilities include lead error or a damaged thread. With fine threads the inspector should be careful to not cross thread the parts.


It is important to use the no go gage as it checks pitch diameter exclusively. It is unaffected by other conditions in the screw thread as it is intentionally truncated on the crests and with greater clearance applied on the roots of the thread. The no go thread plug should not enter the part more than 3 turns although in practice it is advisable to limit the amount of turns to 1 ½ - 2 turns max. The user just simply counts turns. The end user should review the applicable thread specification in detail as there are variations to the above practice.


As stated in ANSI/ASME B1.2-1983, the “NoGo (Lo) functional diameter is acceptable when the NoGo (Lo) thread ring gage applied to the product external thread does not pass over the thread more than three complete turns.” The gage should not be forced. Special consideration such as exceptionally thin or ductile material, small number of threads, etc., may require modification of accepting up to 3 turns of the gage. It is highly recommended that a manufacturer not allow a maximum of 3 turns during thread fabrication as every thread ring gage is set slightly different to due the gage maker tolerances of set plugs and the subjective nature of setting adjustable style thread ring gages.

Below - from Inspection and Gaging - Kennedy- Hoffman- Bond, page 470 but ref. is ANSI B1.1 Unified Screw Threads " The "No Go" end must not enter more than 1 1/2 turns, else the tapped hole is too large.
ANSI/ASME B1.2-1983 revised per above verbiage
RM