This is a proposal to build a haptic interface to a mechanical design system. The objective is to demonstrate that part interaction, assembly, and manipulability can be evaluated without physical prototypes. Visual interactions are provided by a CRT screen, while haptic interaction is by means of force reflecting telerobotic master arms, which the user wears as an exoskeleton. Instead of controlling slave arms in a remote environment, the masters affect a virtual world in which the prototype assembly exists. Geometric and functional reasoning determine part contact, interference, and the propagation of forces and torques. Visual rendering techniques display the current state of the assembly. Haptic rendering techniques feed back appropriate forces to the master arms, enhancing the effectiveness of the interface.