In order to reduce differential pressure sticking, the surface of drill collars can be spiral-grooved. VAM Drilling spiral drill

 Cross sections of the drill collars show the reduced contact area with the wall of the hole.The grooving consists of three right-hand spirals, machined on VAM Drilling’s unique triple-headed milling machines. Stress relief features improve bending strength of pin and box connections and, therefore, durability. Bore back on box and stress relief grooves on pin are defined by API

Professional Spiral drill collar