Hi Martin,

> Sorry Michael, but I couldn't follow this bit:- "You can get the basics of it right now by using
> Edit > Separate on the face, then doing a shell, then deleting the bottom face of the shell and
> then joining it back in." I'm probably having a blonde moment though, but thoroughly
> enjoying using MoI.

Those are just the steps you can do currently to get the same result as what I think you're looking for with the "zero width" inset.

Step 1 - select the face of the solid that you wanted to do the inset on.

Step 2 - run Edit > Separate to break that face off from the main object and make it into its own separate individual surface. This is because the Shell command in the next step operates differently depending on whether you have an unjoined individual surface selected or whether you have a face selected that is joined to other things.

Step 3 - Run Construct > Offset > Shell on the separated surface. When run on a surface shell thickens a surface into a slab.

So now at this point you basically have all the pieces that you were looking for, the only problem is that the shelled surface is a solid with top and bottom caps, so in order to finish it up you will want to delete the bottom face of this solid slab piece and then with the bottom open you can join the main body and the thickened slab piece together again.

In order to get at the bottom face of the slab you will probably want to hide the main piece temporarily. One quick way to do that is by using the "isolate" functionality - select the slab and right-click on the Hide button. Doing a right-click does an "Isolate" operation which keeps the selected object and instead hides everything else. Then when you're done working on that object, do second right-click on the Hide button and it will restore object visibility to the previous state before you did the initial Isolate.

Hope this helps, let me know if it's still not clear.

- Michael