Anchoring device for screws

Claim 1

In an anchoring device for use with wood or machine screws consisting of a generally cylindrical casing in the form of a slitted expansion dowel and an associated, also generally cylindrical, expansion body which is axially displaceable towards the casing by means of a screw that engages the expansion body, in the manner of a nut which is prevented from rotating, for the purpose of expanding the casing in a radial direction, the casing and the expansion body being crossed by axial hollow chambers, and the slits in the casing extending over a region of the casing facing towards the insertion end, and the expansion body comprising suitable wedge-shaped faces to enable it to engage in the slits provided in the casing and thus to press them apart when the expansion body is tightened by means of the screw, the casing and the expansion body both consisting of plastic material and being connected together in the unused state by a connection means which is easily broken by the axial movement of the expansion body when it is tightened by the screw, the improvement which comprises: said casing, wherein each slit formed therein has a closed end formed by a radially extending, inclined surface of said casing, a first portion adjacent the closed end of each slit defined by substantially parallel, longitudinally extending surfaces of said casing, and a second portion adjacent said first portion defined by surfaces of said casing which are longitudinally divergent in the direction of the insertion end of the casing so as to widen an open end of the slit at the insertion end of the casing; and said expansion body, which includes longitudinally extending, wedge-shaped tabs formed on a rear portion of the expansion body, the lateral end faces of each tab being oppositely inclined with respect to one another and forming said wedge-shaped faces for enabling the expansion body to engage said casing within said slits, and said expansion body being axially spaced from, and secured to, said casing by said connection means so that an end portion of each tab projects toward the open end of a corresponding slit of the casing; whereby, as the screw engaging the expansion body is turned in a direction to cause axial movement of the expansion body toward the casing, after the connection means is ruptured and the casing is expanded radially outwards by the engagement and movement of the wedge-shaped tabs within the slits, the wedge-shaped tabs are forcibly deflected radially outwards by the inclined surfaces of the casing which form the closed ends of the slits.