184 may include one or more flow passages 189 formed therethrough for accommodating drill string fluid flow while one embodiment of catch is described as having a cone 184 and balls 180 in other embodiments for example fingers 180 may be pins seated in a piston which pins can be moved radially outward under pressure from within the piston as shown in fig3 a when catch 18 is in the inward disengaged position a second portion of cone 184 having a smaller diameter engages balls 180 thereby allowing balls 180 to be substantially contained within stroke rod in this position cone 184 still captures balls 180 partially within apertures 181 should any ball 180 continue to extend radially outward from stroke rod 110 after catch 18 is disengaged any external force acting thereon such as from first or second hammer 140 145 fig2 b will urge the ball inward as shown in fig3 b when catch 18 extends radially outward from said stroke rod 110 in the engaged position a first portion of cone 184 having a larger diameter engages balls 180 forces balls 180 to extend radially outward from stroke rod 110 while the figures illustrate catch 18 engaging a hammer 140 141 at an end of the respective hammer in other embodiments catch 18 may engage the respective hammer anywhere along the length of the hammer for example a seat or cavity not shown may be provided at.