The workflow for defining part models in Simscape™ Multibody™ is shown for a piston head. The piston can be defined using two pieces of standard geometry and an extrusion defined in MATLAB^®. The mechanical interface to the piston requires frames positioned and oriented corresponding to the connections to the cylinder and connecting rod. Parameterized parts can be reused in other designs and makes it possible to rapidly explore the design space and leverage optimization algorithms to find the best design.