This paper proposes a new method for automatic tuning of the impedance parameters, such that the manipulator control changes automatically from hard control to soft control, for assembly of components. Automatic tuning of impedance parameter for assembly, makes the change of manipulator control form hard control to soft control, smooth and makes system faster. Impedance parameter are tuned with respect to an artificial potential variation generated using configuration space (C-space) and relative mobility of components for assembly. The relative mobility, without collision of the components in configuration space, is calculated for the translational motion and the rotational motion, for each point in the configuration space in 2-D. The mobility potential is calculated by inverting the possible relative motion without collision, between components, for each point in C-space. If the available space for the possible relative motion by translation and by rotation is less, then higher is the potential of that point. When the peg and the hole are in dis-assembled state, relative mobility between peg and hole is large, hence the impedance parameters are large. As peg and hole are aligned for assembly impedance parameter are automatically decreased, using potential created by C-space and relative mobility potential. As the peg and hole are assembled impedance parameter are tuned to achieve force control. Automatic tuning of the impedance parameter is experimentally verified for grasping of hexagonal head bolt by a wrench. Two dimensional model of hexagonal bolt head and wrench is used to calculate the configuration space and the relative mobility of wrench and bolt.