Let's consider the following figure
The grey box contains a blue stick which is fixed. The blue stick has a length of $ a+b+c $ and two diameters $ f,h $. The diameter $ h $ describes the part $ b $ of the stick. The stick is fixed in the plane but the plane is not connected to the grey box. A force $ F $ is pushing against the withe plane like in the picture. How much force is needed to break off the stick in part $ b $?