As an important part of drill string, drill collar can supply the drill bit and increase the rigidity of drill string.
Stand size and thread connection
Cylindrical type drill collar : Be made of alloy steel and the cross sections of the inside and outside pipe are both round.
Spiral Type : Be made of alloy steel and the outside pipe has spiral grooves.
Non-magnetic : Made of stainless alloy steel with rather low magnetic permeability and the cross sections of the inside and outside pipe are both round.
