This paper describes a method for improving commonality in a highly customized low volume product line whose members were originally developed one-at-a-time to meet specific customer requirements. Rather than focusing on redesign of the entire product line, which can often be cost prohibitive, the method is part of a strategy to redesign a limited set of component parts that have the highest potential for cost savings. The method involves a four-step process: (1) determine an optimal component solution for each member artifact of an existing market segment grid, (2) test the feasibility of using each optimal component as a platform for the other artifacts, (3) formulate an optimization problem around the feasibility statistics whose solution is a product platform portfolio, and (4) solve the optimization problem for the minimum number of platforms that can adequately span the existing market segment grid. The proposed method is applied to an example involving the redesign of actuator mounting yokes for an existing set of valves that are used in nuclear power plants. The method shows promise for determining a product platform mix that maximizes commonality yet meets performance requirements.