This is my first post on Reddit so please bear with me lol

I’m an inspector at a machine shop and we have a new customer that makes assemblies for the government (we machine various components for these assemblies.) Most of the drawings are following the 1973 or 1966 Y14.5 standard so most of the GD&T called out had very different meanings from what is done today.

I recently came across a memorandum report by the US ARMY that got released in 1994 and is available to the public. It basically is a translation of standards from 1946-1982 to the Y14.5 1994 revision. I’ll post a photo of the memorandum because I can’t recall where I found it exactly so I don’t have a link if anyone was interested. This has been a lifesaver but it doesn’t answer the issue I’m having with circular runout of threads. 

I don’t want to post a photo of the whole print so I hope the photos I attached will suffice. Even though it appears to be a concentricity tolerance, this is actually a circular runout of an internal STI/Helicoil thread to Datum A (the shaft where the thread was tapped). As per the memorandum I mentioned above, if the callout is RFS then it means circular runout but if it was MMC then it would be position. 

This particular callout will be on internal and external threads and so far I have not seen any with MMC so that means that they want circular runout. There is no mention of major/minor diameters so that means they want it to the pitch diameter. When it comes to internal threads I will use a thread locator but I don’t really know what to do with external threads. How can you measure circular runout of the pitch diameter of an external thread?! Even if you have a tri-roll gage set-up the part will travel as it rotates so it’s not possible to capture circular runout. 

When I’ve looked into this, the only thing I can find out relating the circular runout of a thread is this:

“Runout Per ASME B1.7-2006 Definitions [ back to main page ]

Runout: as applied to screw threads, unless otherwise specified, this term refers to circular runout of the major and minor cylinders with respect to the pitch cylinder.  Circular runout, in accordance with ASME Y14.5M, controls cumulative variations due to eccentricity and out-of-roundness.   The amount of runout is usually expressed in termsof full indicator movement (FIM).”

This doesn’t seem to apply because all of the datum’s are not related to the threads

My other frustration with this is why would you want to know what the circular runout of a thread is in the first place?! It seems like position would make more sense but I don’t know what to think anymore. 

Does anyone out there have any insight on this? 

Circular Runout on Threads