Thx for your help. I managed to get it right once after several attempts. It seems that finding the center of the bottom face is not easy for me. If there are many ways to do it, is there an easier way? I know that modeling should be done so that I wouldnt have to move the groups. This is a simplication of the model. At least for me it is not possible to create my model in one entity. The image in the op is not showing the gap between the two groups