Fixed Fastener Formula - ASME Y14.5

The way I read your question is your trying to understand how a tolerance was divided between the two mating parts.

May I suggest looking at the tolerance of the threaded part as something that may not be in the control of the designer. As a result, the designer may have allowed more tolerance in his part of the equation as a 'feel good' measure.

I struggle with that every day as my fellow engineers don't truly calculate what tolerance to apply but they use their gut feel as to what to put on the drawing. Often this results in tighter tolerances that is required and higher piece price costs.

If your calculating you tolerances correctly, I suggest you don't dwell on the errors of others.

I have found out that there are three different communities (designers/draftsmen, engineering analysts, and design researchers) using vastly different tools and techniques. Cultural and education differences between these communities have kept them isolated from one another and unaware of the other's techniques. The draftsmen community uses a manual procedure called Min/Max Tolerance Charts; this method is true to Y14.5 but can do only worst-case analysis, and in only one direction at a time.

The engineering analysis community uses computer-aided tolerancesoftware (CATS), such as Mechanical Advantage, VSA, 3DCS, e-TolMate. These can do both worst case and statistical analyses, but because they are based on the parametric approach, they have the limitations mentioned previously, such as partial compatibility with Y14.5. Some CATS systems use the same parametric equations as those used in building the CAD model, while others build an abstracted feature model specific to each analysis case. Emerging methods, such as T-maps claim to have overcome the problem of compatibility with standards while providing full 3D worst case and statistical analysis.

Regards

Just find the virtual size of the fastener installed, that will determine your smallest hole.