It would be great if there was a way to accomodate using 2 different size clearance holes, as is necessary when using a shoulder bolt. You need a clearance hole on the top layer for the shoulder, a smaller clearance hole for the second surface (which the shoulder rests on), and then a nut on the bottom surface.
To broaden the suggestion: It would be great if in the IFX references dialogue, there was an advanced option that allowed for non generic fasteners like shoulder bolts, anchor nuts, barrel nuts and others that require more than just a surface and axis reference (that aren't uniform around an axis).
