OK thanks Michael.

The attached file "Bool_Test" shows what I mean.

If you highlight the extruded square bar and also highlight the first extruded cylinder and select "Boolean -> Union" in Moi - and then remove the pieces of the cylinder outside the bar you will see that no piece of the first cylinder is left inside the bar.

And if you then repeat the procedure with the second cylinder then you will find that there is a portion of the cylinder left inside the bar. This is the behaviour that I expect.

This is how I am drilling holes in solids and it gets a bit tedious when I have many of them ;-)

Any thoughts?

Roger