There are different kinds of drill collars,including round drill collar,spiral drill collar,non-magnetic drill collar,square drill collar and so on.Ordinary drill collar is the circular cross
section, the center has a water hole,the wall thickness is larger,the nozzle is smaller, the weight of per unit length is greater than the size of drill pipe almost 4- 5 times .The majority of
drill collar is thread processing directly on the pipe body , but some of them also use the replaced joint.
