Bonus Tolerance for Threads

In this Question Line video, Jason answers the submitted questions below, discussing bonus tolerance for threads and exploring what happens when threaded features are controlled at MMC.

Can threads utilize the bonus tolerance modifier? Can a pattern of threaded features be used as a datum?

In this video, Jason walks through the above drawing containing a pattern of threaded holes controlled by position relative to Datum Reference Frame AB. This datum reference frame is created from Datum Feature A, the back surface of the part, and Datum Feature B, the inner diameter of the center cylindrical feature. Each threaded hole has a diametric position tolerance at MMC, along with a “MINOR DIA” designation that tells us how the controlled axis is established. 

Jason takes a closer look at what the “MINOR DIA” designation means and why it matters when inspecting threaded features. He also looks at whether using the MMC modifier on the threaded holes actually provides any useful bonus tolerance—and whether it is even functionally driven. 

He then alters the drawing, identifying Datum Feature B as the pattern of threaded holes, and discusses how the MMC modifier can now be used to create a fixed functional gage for inspecting the part.  

Watch the video to see Jason work through both scenarios, explaining how the MMC modifier affects the threaded holes and the importance of the “MINOR DIA” designation when controlling threaded features. 

For more information regarding GD&T for threaded holes, see: 

Common Thread Information: Diameters, Pitch, and Threads per Inch 

Position – Controlling Threads on Features 

How to Measure a Threaded Hole 

Why You Shouldn’t Apply Bonus Tolerance Modifier to Threaded Holes 

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https://www.gdandtbasics.com/share-your-gdt-questions/       

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