Linear motion guide unit with buried plug

A linear motion guide unit comprising;

• a guide rail having lengthwise sides on which first raceway surfaces extend lengthwise of the guide rail and a lengthwise top surface having bolt holes used to fasten the guide rail to any other component, the bolt holes being provided with counterbores spaced apart from each other at a preselected interval, a slider that fits over or conforms to the guide rail for movement relative to the guide rail, the slider having second raceway surfaces lying in opposition to the first raceway surfaces of the guide rail to define load-carrying races between the first raceway surfaces and the second raceway surfaces, a plurality of rolling elements allowed to roll through the load-carrying races as the slider moves relative to the guide rail, and buried plugs which fit in the counterbores to close the counterbores;
• wherein the buried plug has a mating zone having an outside circular portion to press fit into the counterbore of the bolt hole and a leading zone integral with an end of the mating zone to guide the buried plug into the counterbore of the bolt hole;
• and
• wherein the mating zone has an interference with the counterbore, the interference being lopsided over all the circumference of the counterbore, and further under a definition that a direction perpendicular to a lengthwise direction of the guide rail is referred to a widthwise direction of the guide rail, the interference exerting a force on the counterbore in the widthwise direction is determined less than the interference exerting the force on the counterbore in the lengthwise direction of the guide rail.