A tubular pipe string element having: a first end with a male connector formed thereon, a second end having a female connector formed thereon which is complementary to the male connector, said male and female connectors being of the rotational connector type such that, in use, the male connector is engageable in a female connector of another pipe string element and rotatable relative thereto in a first direction in order to secure the connection and in a second direction in order to release the connection, and complementary anti-rotation means associated with said male and female connectors which anti-rotation means cooperate to prevent unintentional relative rotation between male and female connectors in the second direction; wherein said anti-rotation means comprises: at least one saw-tooth profiled, radially extending tooth having a shallow leading tooth flank angle facing in one of said first and second direction and a steep trailing tooth flank angle facing in the other of said first and second directions formed on the pipe string element proximate one end thereof in association with the male connector, and at least one detent member formed on the pipe string element proximate the other end thereof in association with the female connector, wherein the at least one detent member comprises at least one locking member supported on the female connector by at least one spring arm which urges the at least one locking member into a position in which it protrudes from a surface of said female connector so as to lie in the rotational path of the at least one saw-tooth profiled tooth, said at least one locking member being retractable out of said path against the spring force of the spring arm upon engagement with the leading flank of the at least one tooth, said at least one saw-tooth profiled tooth and said at least one detent member being rotationally and axially fast, with the pipe string element wherein, in use upon relative rotation in the first direction between engaged male and female connectors, the leading flank of the at least one saw-tooth profiled tooth engages with the at least one locking member of the at least one detent member, urging it to retract against the spring force of the spring arm and allowing the connectors (1,10) to rotate into a fully connected position, the steep trailing tooth flank being trapped by the at least one locking member of the at least one detent member when in the fully connected position so as to prevent unintentional release of the connection; characterised in that the or each spring arm is integrally formed with the pipe string element by at least one through cut (5a,5b,5c) in a wall of the pipe string element, such that a through opening is formed in the tubular wall of said female connector inside which the locking member engages. a first end with a male connector formed thereon, a second end having a female connector formed thereon which is complementary to the male connector, said male and female connectors being of the rotational connector type such that, in use, the male connector is engageable in a female connector of another pipe string element and rotatable relative thereto in a first direction in order to secure the connection and in a second direction in order to release the connection, and complementary anti-rotation means associated with said male and female connectors which anti-rotation means cooperate to prevent unintentional relative rotation between male and female connectors in the second direction; at least one saw-tooth profiled, radially extending tooth having a shallow leading tooth flank angle facing in one of said first and second direction and a steep trailing tooth flank angle facing in the other of said first and second directions formed on the pipe string element proximate one end thereof in association with the male connector, and at least one detent member formed on the pipe string element proximate the other end thereof in association with the female connector, wherein the at least one detent member comprises at least one locking member supported on the female connector by at least one spring arm which urges the at least one locking member into a position in which it protrudes from a surface of said female connector so as to lie in the rotational path of the at least one saw-tooth profiled tooth, said at least one locking member being retractable out of said path against the spring force of the spring arm upon engagement with the leading flank of the at least one tooth,