The 3DHM system represents the workbench for the geometric modification, which is part of the PROGIMM platform. The 3DHM system is made up of a visualization system, which is both stereoscopic and semi-immersive, and has been completely developed by PoliMI within the FP6-IST SATIN project. It allows the user to see contemporaneously both the virtual object and his/her hands, with the aim of rapidly and intuitively modifying the geometries under analysis. The effective modification of the geometries is possible by using a 3DOF haptic device. This device has been integrated in order to permit a force feedback while the user id modifying the object. The interaction and visualization metaphors of the virtual model have been studied and carried out to provide a useful tool to be daily used by designers and that allow the user to modify the object properly and according to the model under analysis.