As you say extruding a polygon on a plane has no issues with holes fully cutting and where the cylinders are the same height with no vertical offset that's trivial too (I just add "2" to the length). The problem with the hole lengths comes in when using hull to fill in the space between the cylinders and the cylinders are either different lengths, vertically offset or both so that there are sloping sections between the two cylinders meaning the holes are cutting through a sloping face so need to be longer than their "parent" cylinder. Chris Johnson >