Provided are various embodiments of structures that may utilized in a power driver, particularly in a power driver having an optional reciprocating “hammer” action, that may be utilized for retaining an outer bearing during driver assembly and during subsequent operation of the power driver. In particular, the disclosed structures provide one or more surfaces, particularly inner peripheral surfaces, that limit the outward axial movement of the bearing. These structures may include combinations of surfaces defined by retaining members including, for example, one or more flanges, clips and threaded members, an input shaft, biasing mechanisms, typically a spring or other resilient structure, and chuck shield assemblies for positioning the outer bearing within the power driver.