The planting of individual sea grass plants or small bunches of sea grass plants is known in the prior art. The cover is pivoted to the body, such that the cover is open relative to the body, and therefore elements in the body are exposed. The axial dimension of the inner spacer sleeve is elongated slightly relative to an axial dimension defined between outboard faces of the installed retaining rings, thereby slightly unloading the sets of bearing balls from their respective outer bearing races.