Selecting appropriate tools for car assembly lines usually demands hours or even days of expert tool engineers consulting catalogues, examining the joint properties and studying technical guidelines or specifications. The number of available alternatives, the great number of parameters defining the joint and tool, and uncertain and sometime perceptional and heuristic nature of tool selection knowledge, makes this process inefficient and sometimes faulty. The mainstream of the studies in this field have been limited to geometrical accessibility analysis of the joints and despite crucial effect of many other tool parameters they have been rarely taken into account. In this research, majority of selection parameters are considered which help make the tool assignment process more realistic. Regarding the structure of the problem and the characteristics of the existing strategies, expert systems are used as an efficient alternative. A rule based expert system is proposed to perform tool assignment task. The devised interactive system assigns the propers tool to the targeted operations with reliability and speed. It reduces the time and cost pertaining to process planning for new products and hence increases competitiveness in automobile industry. It also can be used in many other industries that include threaded joining operations.