Abstract: A wrench for removing and installing cylindrical retainers, particular sight glass retainers comprises a base member, a guide member and a pair of projections. The base member has a planar stop surface on one axial end. The guide member is fixed to the base member and extends perpendicularly from the stop surface. The projections extend in opposite directions from the guide member parallel to and over the stop surface. When coupled to a sight glass retainer, the stop surface engages an exposed axial end portion of the retainer, the guide member engages the retainer inner cylindrical surface, and the projections are received within diametrically opposite recesses in the retainer end portion.