Abstract: A metal cap covers the open end of a sleeve, forming the hub of a roller for a tracked vehicle, to form en enclosed oil bath for the bearings where the cap includes on a center domed section a center opening covered by a transparent window for viewing of a level of oil in the bath and has a first and a second filler opening each closed by a screw plug where the filler openings are arranged generally on opposite sides of the center opening such that generally one of the openings will be available for filling above a horizontal line passing through the center of the domed section.