Self-centering hole adapter

The invention provides a self-centering hole adapter. The self-centering hole adapter has high stability when used for installing a prism fixedly. The self-centering hole adapter comprises a hollow base, wherein a spring and a core shaft are arranged in the hollow inner part of the base; a positioning cone is arranged on the lower part of the core shaft; and the spring is sleeved on the core shaft and is positioned at the upper end of the positioning cone. In the self-centering hole adapter, an installation device for the prism is arranged by utilizing bolt holes for arranging rail fasteners directly, so that the error of the spatial attitude, which is reflected by the prism, of rail plates can be reduced to the minimum; and the self-centering hole adapter is close to the bolt holes, so the relationship between the central position of the prism and the bolt hole is stable. Simultaneously, the self-centering hole adapter is small in volume, and the influence of ambient temperature on the stable relation is limit, so the relation is not needed to be checked in the using process; and the self-centering hole adapter can be matched with the bolt holes on different rail plates and can be used for measuring the rail plates and also can be used in other fields.