Abstract: A retainer for a pneumatic tool and assembly therefor is disclosed. The retainer includes a tool body having an internal surface defining a bore and an external surface having a threaded portion. A retainer cap is used with the tool body and includes an internal surface having a threaded portion adapted to engage the threaded portion of the tool body. An insert having an outer surface is rotatably mounted in the retainer cap. The insert includes an inner surface with a first inner surface portion adapted for conforming with a non-circular lug surface of a tool shank and a second inner surface portion radially offset from the first portion adapted for conforming with the non-circular lug surface.