A device for adjustably controlling the position and set-back of a piston rod which extends from a damping cylinder used on an airfeed peck drill. The device includes a plurality of ball members which surround the piston rod. The ball members are positioned against the piston rod by a spring biased cone having a tapered internal surface. The balls are further positioned with respect to the cone by a spring biased ball separator which is movable with respect to the cone by air pressure. The travel of the piston rod is made adjustable by a nut member threadably engaged with the housing.
