API 7 pdf download.Specification for Rotary Drill Stem Elements 3 Definitions For the purposes of this specification, the following defini- tions apply: 3.1 bevel diameter: The outer diameter of the contact face of the rotary shouldered connection. 3.2 bit sub: A sub, usually with 2 box connections, that is used to connect the bit to the drill stem. 3.3 box...