surface 40 having radius r 3 which connects opposite faces 26 28 of each tooth or spline 22 the amount of truncation is approximately u2153 of the depth of the rib or tooth 22 to define a radius r 2 thus the truncated section 42 of tooth 22 is defined by three surface facets or faces namely the partial faces 26 28 and the truncated face 40 the longitudinal extent of the end section or truncated tooth section 20 is approximately one half of the longitudinal extent of the midsection 18 a typical radius r 2 associated with the apex 24 is in the range of 0 23 u00b1 0 005 inches as depicted in fig6 the manner of use of the tool requires positioning the ribbed or splined sections 18 20 into the portion of the broken coupler 50 retained within the engine block 52 in a manner which aligns the axis 10 with the center line axis 54 of the coupler 50 the tool is then driven down into the coupler 50 in a manner which engages the crests of the peak 24 of the teeth 22 with the coupler 50 that is the truncated portions or section 20 of the ribs teeth or crest 22 form an initial guide mechanism or pathway for movement of the tool into the opening defined by the broken coupler 50 the crest 24 of the teeth 22 then will be driven into the coupler 50 by engaging a hammer 53 against the surface 14 thereafter a wrench pliers or the like is gripped on the polygonal head 12 and the coupler 50 is unthreaded from the engine block variations of the tool may be implemented for example the size and array of.