PURPOSE: To always make correct sizing of a table by freely regulating an excessive backlash produced between a spiral shaft and a female screw piece of a basement bearing.

CONSTITUTION: A bolt 5 which screw-engages one female screw piece 3 of a basement bearing 2 of a table 7 screw-engaged with a spiral shaft 1 with the vicinity of a slit part 10 of the basement bearing 2 is tightened to fix the female screw piece 3 to the basement bearing 2. Subsequently, a bolt 6 opposite to the other female screw piece 4 is loosened to enable spiral movement of only the female screw piece 4. Thus, a tool such as a spanner or the like is locked in a bearing hole 15 formed on a flange part 16 of the female screw piece 4 and turned in the direction of approaching one female screw piece 3 which fixes the female screw piece 4 to adjust backlash formed by such a clearance as to produce play to backlash of designated dimensions. Subsequently, the loosened bolt 6 is tightened to fix the female screw piece 4 to the basement bearing 2 so that the table 7 can be advanced and retreated by accurate screw- engagement without any play.