FIGURE STRUCTURE / HIERARCHY

The BookStack4 figure has six bones/bodyparts in a chain:

Body > Stack > Book1 > Book2 > Book3 > Book4 > TopOfStack

The first bone/bodypart (Stack) and last (TopOfStack) have no associated geometry and all their parameters are fixed (force limits is set and the minimum/maximum limits are the same) and the dials are hidden. The reason for the 'Stack' bone is explained in post #67 of the HiveWire3D topic (basically the joint parameters are different for the first bone and I couldn't do what I needed) and the reason for the TopOfStack bone in post #66 of the HiveWire3D topic (basically ensures that a nested child stack will respond correctly when the thickness of the top book changes).

The remaining four bones are for the four books. Here's the hierarchy for a single figure:

and four a stack of two figiures, the second being parented to the TopOfStack bone of the first.

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The 3Dcheapskate (also available in DAZ and HiveWire3D flavours) occasionally posts sensible stuff. Usually by accident.
And it usually uses Poser 11, with units set to inches. Except when it's using Poser 6 or PP2014, or when its units are set to PNU.