This paper describes an haptic system designed to vary the stiffness of three contact points in an independent and controllable fashion, by suitably regulating the inner pressure of three pneumatic tactile displays. At the same time, the contact forces exerted by the user are measured by six degree-of-freedom force sensors placed under each finger. This device might be profitably used in hand rehabilitation and human grasping studies. We report and discuss preliminary results on device validation as well as some illustrative measurement examples.