a pivoting exterior rearview mirror assembly comprises a mirror housing , a base , a support frame , a pivot assembly , and associated elements comprised primarily of a plastic or polymeric material . the pivot assembly is provided with a pivot reinforcement made of a relatively high - strength material , such as steel . the base is provided with a cantilever reinforcement made of a relatively high - strength material , such as steel . the reinforcing steel increases the load carrying capability of the plastic and reduces the potential material failure of unreinforced plastic .