First, I want to give a shout-out to Andy Davis, from the AutoCAD Plant 3D Forum for providing this solution.

To change the bolt lengths to imperial, you need to make a couple of changes to the isoconfig.xml file.

At the end of the <Styles> section, add the following style tag:

<Style Name=”MetricBoltSize” UnitFormat=”Fractional” Precision=”Precision5″ Prefix=”” Suffix=”&quot;” Scale=”0.03937″ Decimal=”.” />

Then modify the BoltLengthStyle tag as follows:

<BoltLengthStyle Imperial=”ImperialSize” Metric=”MetricBoltSize” Rounded=”true” />

That’s all you need to do.