the bulges 35 keep working the redundant debris is capable of being smoothly extruded out of the object 2 along the extrusion path 351 as plainly arrowed in fig8 by means of the existing of the extrusion path 351 the debris would in turn to be pushed toward the extrusion path 351 and be progressively guided out of the object 4 when it is impeded by the bulges 35 and which accordingly facilitates decreasing the drilling torque and achieving a speedy screwing as well as avoids the broken of the object 4 by the guidance of the extrusion path 351 that prevents the occurrence of excessively accumulating debris and of the forced jam of the debris within the threads 33 still referring to fig7 after screwing the screw 3 into the object 4 the remain debris shown by the dots which is not extruded out of the object 4 distributively and consecutively fills with the threads 33 namely among the extrusion path 351 and the bulges 35 so that the screw 3 can achieve a preferable firmness within the object 4 as the installation of the bulges 35 would not affect the amount of the remained debris accommodating between the threads 33 moreover the unsevered fibers shown by irregular solid lines with the elasticity.