The Drill collar for oil well drilling are manufactured strictly comforming with API Spec7-1. 4 major types: Slick drill collar, Spiral drill collar, Spiral Drill Collar w/ Elevator Groove and Slip Groove, Non-magnetic drill collar. Material: AISI 4145H, 4145H Mod and Non-magnetic material. Size: OD: 3 1/8?~11?? ID: 1 1/2?in. Length:10?~31?? Elevator groove and slip groove made on box thread face of slick drill collar or spiral drill collar can be used as lifting sub and safety slip when trip out. Hardbanding is optional at customers' requests. More details of products,you are welcome to contact us by mail,thanks!