A clamp shank device designed particularly for attaching a chisel type of plowshare, cultivator blade, or the like to the draft frame of an agricultural implement includes a resiliently-biased clamping arrangement confining a shank member against lateral tipping movement but permitting it to ride up and over obstructions. The shank member is rectangular in cross-section and has a forward, horizontal, attachment portion rigidly held flatwise against the upper face of a rocker plate whose rearward end is beveled downwardly and forwardly to provide an upper pivot edge across the width of the plate. Such pivot edge is received by and extends along the vertex of a forwardly and downwardly facing angle included between the steps of a bottom-stepped rear wall of a supporting frame that is adapted to be attached to and beneath a tool-carrying member of the implement draft frame. The rocker plate is spring-biased upwardly at its forward end toward a top wall of the supporting frame and is free to move downwardly at that end against spring tension while pivoting against the frame on and along the pivot edge of its rearward end, within the vertex of the receiving, included angle of the frame. Any tendency toward lateral tipping of the shank during normal working conditions is minimized by a cinching clamp at the rearward end of the frame.