A closure assembly for a camshaft phaser. A plug or a cap is provided with either a radially-sealing gasket seal or a face-sealing gasket seal, the seal being formed by insertion of the plug into a bore, or by installation of a cap over a neck formed in a cover plate. The closure is provided with a plurality of spaced-apart locking elements, and the plate is provided with a plurality of spaced-apart, radially extending second locking elements in the form of fingers surrounding a central opening. During assembly, the closure is mated to the plate with the first locking elements interspersed with the second locking elements. The closure is rotated to bring the locking elements into locking engagement with each other, preventing counter-rotation of the closure. No threads or torque specifications are required.