2B nut on 3B gage

[liquidsords]

I am trying to inspect a 3/4-10 UNC-2B capnut for use with a 3/4-10 UNC-3A plain stud. The 2B cap nuts will thread on to the 3A studs that I have, but will not even begin to thread on to the 3B gage that I am using to check them. I figure that there must be a reason but I can't explain it. Any ideas?

 

[BillPSU]

I would almost bet the stud and nut are 3/4-16UNF not 3/4-10UNC. Take a rule and measure the pitch or get a thread pitch gage. Studs are typically fine threaded.

If I am wrong which happens frequently, verify the plug gage has the correct ends install into the handle. Check the thread per inch especially. If all else fails, gage the stud as a final check.

 

[cougfan]

A 3B thread is a close fit thread. 3B's have a tighter tolerance on pitch diameter.

The pitch diameter of the 3/4-10 UNC 2B thread is as follows: .685/.6927
The pitch diameter of the 3B is .685/.6907.
Therefore, your cap nut may have a pitch diameter at or above .6907, but below .6927.

 

[cougfan]

Sorry, I was thinking backwords...woops.
Please dis-regard