Abstract: An earth borehole instrument has a plurality of wear link members adapted to engage the borehole walls which are pivotally attached through articulated mechanical arms both to a fixed collar and to a spring-loaded slidable collar on the instrument. The articulated arms for each wear link member consist of a pair of power arms which are each pivoted at a center point on the wear link adapted to engage the borehole wall and a pair of sensing arms which are pivotally connected, respectively, to the ends of the wear link. In an alternative embodiment, a bow spring is mounted on the underside of the power arms for maintaining the wear link flat against the borehole wall.