Abstract: A drill string includes a plurality of tubular members each having a connection with a pin connector and a box connector on adjacent tubular members. The pin connector has an external thread adapted for threadingly engaging an internal thread on the box connector of the adjacent tubular member. The pin connector has an outer groove for receiving a protuberance on the terminal end of the box member. The protuberance and groove have contoured surfaces providing large metal-to-metal contact for preventing the contoured surfaces from sliding during over-torquing and cyclic bending of the drill string.