Drill string element and detachable driving element

A drill string assembly comprising:

• a drill string element adapted to be held by drill pipe rams of a blowout preventer to enable the drill string to be disconnected at the blowout preventer, the drill string element comprising:
• a housing portion adapted to be engaged and held by the drill pipe rams of a blowout preventer, the housing portion defining a longitudinal bore along a longitudinal axis of the housing portion;
• at least one recess arranged in the longitudinal bore, said at least one recess arranged to engage at least one lug of a detachable driving element arranged to be disposed in the longitudinal bore to rotationally lock the housing portion and detachable driving element together;
• at least one first guide surface arranged in the longitudinal bore, said at least one first guide surface arranged to slidably engage with said at least one lug when said detachable driving element is advanced along said longitudinal axis in a first direction to cause said detachable driving element to rotate through a first angle relative to the housing portion about said longitudinal axis;
• and
• at least one second guide surface arranged in the longitudinal bore, said at least one second guide surface arranged to slidably engage with said at least one lug when said detachable driving element is retracted along said longitudinal axis in a second direction, opposite to said first direction, to cause said detachable driving element to rotate through a second angle relative to the housing portion about said longitudinal axis to a position in which further retraction of said detachable driving element causes said at least one lug to bypass said at least one recess to enable the detachable driving element to be removed from said longitudinal bore and detached from said housing portion;
• and
• a detachable driving element adapted to detachably engage the drill string element, the detachable driving element comprising:
• a shaft portion;
• and
• at least one lug disposed on said shaft portion, said at least one lug arranged to be disposed in at least one recess of a longitudinal bore of a housing portion of said drill string element to rotationally lock the housing portion and detachable driving element together.