A spool and wobbler assembly for a sprinkler includes a spool section with facing spool flanges on opposite sides of a spool core, where at least one of the spool flanges includes a circumferential rolling ledge. A wobbler cage including a wobbler ring is supported on the spool section, and a water deflector plate is coupled with the wobbler cage. An underside of the wobbler ring is provided with a circumferential rolling surface that engages the circumferential rolling ledge of the at least one spool flange. The rolling surface and rolling ledge provide for smoother orbital motion of the deflector plate.