Expandable anchor stud

Claim 1

An anchor stud adapted for insertion into, and clamping attachment against a cylindrical bore, the anchor stud comprising: a central threaded member defining a longitudinal axis and a front and rear end of the stud said rear end having tool engaging means thereon, whereby said front end is adapted to be inserted into said cylindrical bore; a pair of oppositely tapered expansion plugs arranged on the threaded member in a concentric, axially spaced relationship near its front and rear ends, the respective tapers of said plugs converging toward each other, the rear expansion plug being axially slidable on said threaded member means for causing the front expansion plug to be displaced in a rearward direction; an expandable shell assembly comprised of a plurality of separate arcuate shell segments of equal length mounted about the stud with the front and rear expansion plugs at opposite ends thereof, whereby said shell segments cooperate with the tapers of said front and rear plugs, respectively; an external peripheral groove on said shell assembly, said groove having a broad and shallow rectangular cross-section; said groove being located axially closer to the rear end of said shell assembly than to the front end of said shell assembly; a coiled spring means positioned within said groove surrounding and radially retaining the segments of said expandable shell assembly; and means on said rear expansion plug for limiting axial displacement and radial expansion of said shell assembly at the rear expansion plug; whereby the off-center location of said groove prevents rearward shifting and premature expansion of said shell assembly during insertion, whereby said spring member assures maintaining a concentric arrangement of said shell segments during handling, and whereby non-uniform expansion and distribution of clamping force is achieved.