Spiral grooves let mud circulate freely around the drill collar to equalize pressure and prevent a seal from forming. The reduces the occurrence of differential pressure sticking,Spiral prevents differential sticking without spiral. Spiral collars are wide used because of their maintenance features.The special grooves decrease the volume of the contact between the well side and the pipe, it leads to the decrease of the "tack" of the pipe and to turning of the drill pipe string. The weight of round drill collars will be reduced approximately 4-6% by spiral conversion.