Jim, It's a little hard to tell from your submission what's going on (what's solid, what's surface, etc.) In any case, there a many ways to do such things, probably two in particular. First create a surface which is offset "inward" by 3mm from the angled surface. Now either (1)create an extruded shape To Selected and pick the new surface, or (2) create an ordinary extrusion, pick its end surface afterward, then select Edit/Replace and again pick the new surface. You could also trim back a longer extrusion using the surface (Solidify). David