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Thread Size Question

SomeGuy

SomeGuy

Hobbyist
Diameter is 1.25 inch. Thread is 28 UN-2B. Pitch diameter: 1.2280 inch minimum; 1.2330 inch maximum.

Can someone help decipher this spec? maybe link a tap that would cut this if such a thing exists?
 
I am probably wrong, but the diameters are the nominal measurements of the major diameter (outside peak of the thread) the minor diameter (inside valley depth. The pitch is the mid thread diameter that represents the pitch.

The final 2B I believe is the tolerance to dimension... aka the fit. If it dont fit you must acquit, or toss it and find a new srcew

A tolerances are external threads on bolts etc, B tolerances are internal on nuts
 
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SomeGuy said:
Diameter is 1.25 inch. Thread is 28 UN-2B. Pitch diameter: 1.2280 inch minimum; 1.2330 inch maximum.

Can someone help decipher this spec? maybe link a tap that would cut this if such a thing exists?
Click to expand...
I couldn't fins 28UN taps at any of my usual sources for taps. Making one may be your best option.
 
Here is the relevant page in machinery's handbook.

20240821_124015.webp

20240821_124357.webp

Couldn't really get the whole thing in and still be legible so the red highlight identifies the 1.25-28 thread specs. Both 2B and 3B are listed.
 
SomeGuy said:
It's for some bad threads in aftermarket Shure microphone grills, I got the spec from here:

If it's 28 pitch, I think I can just clean them up single point on the lathe carefully (not under power).
Click to expand...

FYI to those who find this, single point worked...was quick, just pick up the thread and ran it through a couple times manually and they thread ok.

The bottom of the thread was just misformed, like they stopped feeding the threading tool while still turning, which is why the things would stop threading on as soon as they hit that spot but everything up to that point was fine...so I lost a half a turn of threads cleaning them out at the bottom, but zero impact on retainment of the microphone ball.

Problem solved :)


(double FYI, only reason I picked up some aftermarket grills rather than OEM ones, is the OEM (Shure) don't make colourful ones, I wanted gold ones for some participants in something I'm doing in September so they can have the "golden mic" lol)
 
SomeGuy said:
I have machinery's handbook and didn't even think of looking in there lol I got hung up on the 2B thing as I had never seen that before.
Click to expand...

Hey, we all do that from time to time! All we can do is laugh at us!
 
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