Apparatus for attaching a member onto a planar surface of an object within a predetermined degree of positioning accuracy relative to a reference axis on the planar surface. The apparatus comprises first and second bores in the object that are spaced a predetermined distance apart on the reference axis such that their respective centers extend substantially perpendicularly through the reference axis. First and second hollow protrusions are formed on a mating surface of the member and are spaced apart on the mating surface a second predetermined distance and are shaped such that the second predetermined distance can vary a predetermined amount relative to the first predetermined distance without affecting the ability to simultaneously insert the first and second protrusions into the first and second bores, respectively, while maintaining the degree of positioning accuracy of the member relative to the reference axis on the planar surface on the object.