yielding for an effective interlock this technique will hereafter be referred to as the 34 peening 34 process a mechanism which makes the peening process even more successful is the interaction between the relatively hard cutter threads 40 and the relatively softer threaded ring threads 46 as forces present during drilling attempt to loosen the threaded ring 42 the softer ring threads 46 are pushed over the deformed cutter threads 40 during this motion a small segment of the threads 46 themselves becomes permanently deformed this additional deformation further increases the effectiveness of the present invention as will be described in more detail later laboratory testing has shown breakout torque for peened assemblies ranges from 100 to 120 ft lbs increasing to more than 200 ft lbs during the first revolution bits run in the field assembled with the peening technique are very difficult to disassemble and those that are disassembled are severely damaged in the process any means of effecting a significant change in the shape of the cutter 39 s threads without significant loss of material will result in satisfactory mechanical interlocking in the sense that there are many ways to cause this change any deliberate action which causes physical distortion of the threads even if.