I've just noticed that this seems to be standard - when you go into the Setup room the first bone in the skeleton, the one directly parented to 'Body' (so usually 'Hip' for a humanoid figure, but plain old 'bone_1' in my example below) doesn't have the x/y/zRotate joint parameters that all other bones have.

Here's an example, a 2 bone figure created in Poser's Setup room from an imported OBJ file consisting of two cubes.

Bottom cube's grouped to bone_1 and has only 2 joint parameters that I can edit.

Top cube's grouped to bone_2 and has five parameters

I need to be able to set up the x/y/zRotate joint zones for the bottom cube/bone_1.

How can I do this ?

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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.