Abstract: A plurality of thin plates of metal is mounted on the central raised surface portion of a collar formed by semicircular annular members that are hingedly secured together. Each of the plates includes a blade portion to contact the well bore wall; a pair of spaced legs formed by spaced strips extend from one edge of the blade portion in generally a plane transverse to the blade portion, each of the legs including: a first portion having openings therein for securing one each of the plates in one each of the openings; a second portion extending upwardly from the first portion and outwardly through the opening; and a third portion extending transversely of said second portion and forming a juncture with the blade portion along a plane generally parallel with and elevated above the central collar surface so that flexing of the blade portion is generally along the juncture of the third portion and blade portion in a plane above the raised central surface of the collar.