An anti-rotation system (10, 10B-10G) for use in retaining a threaded connection between first and second tubulars comprising: a recess (16, 16A16G) in a side of the first tubular adjacent the second tubular; and a generally planar key (24, 24B-24G) mounted in the recess (16, 16A-16G), and rotatable between an unlocked and a locked position in response to relative rotation between the first and second tubulars in a decoupling direction (A1, A2), the key (24, 24B-24G) comprising: a non-circular perimeter; an outer edge (30, 30B-30G) on a portion of the perimeter in contact with a radial surface (31, 31B-31F) of the second tubular when the key (24, 24B-24G) is in the locked position and when the key (24, 24B-24G) is in the unlocked position; and a lateral edge (25, 25C-25G, 42E, 58) on a portion of the perimeter that is in interfering contact with a side wall (18, 18B-18G, 20E, 22F) in the recess (16, 16A-16G) when the key (24, 24B-24G) is in the locked position, and so that when the first and second tubulars rotate in the decoupling direction a resistive force from the side wall (18, 18B-18G, 20E, 22F) to the lateral edge (25, 25C-25G, 42E, 58) transfers to the second tubular to rotationally couple the first and second tubulars; wherein the outer edge (30, 30B-30G) comprises at least one tooth that projects outward from the key (24, 24B-24G) and bites into the radial surface (31, 31B-31F) of the second tubular and transfers the decoupling force to the second tubular; wherein the recess (16, 16A-16G) is formed along a portion of a circumference of only the first tubular (12, 12A-12G), characterized in that the radial surface (31, 31B-31F) of the second tubular is normal with an axis (Ax) of the first tubular and the second tubular. a recess (16, 16A16G) in a side of the first tubular adjacent the second tubular; and a generally planar key (24, 24B-24G) mounted in the recess (16, 16A-16G), and rotatable between an unlocked and a locked position in response to relative rotation between the first and second tubulars in a decoupling direction (A1, A2), the key (24, 24B-24G) comprising: a non-circular perimeter; an outer edge (30, 30B-30G) on a portion of the perimeter in contact with a radial surface (31, 31B-31F) of the second tubular when the key (24, 24B-24G) is in the locked position and when the key (24, 24B-24G) is in the unlocked position; and a lateral edge (25, 25C-25G, 42E, 58) on a portion of the perimeter that is in interfering contact with a side wall (18, 18B-18G, 20E, 22F) in the recess (16, 16A-16G) when the key (24, 24B-24G) is in the locked position, and so that when the first and second tubulars rotate in the decoupling direction a resistive force from the side wall (18, 18B-18G, 20E, 22F) to the lateral edge (25, 25C-25G, 42E, 58) transfers to the second tubular to rotationally couple the first and second tubulars; wherein the outer edge (30, 30B-30G) comprises at least one tooth that projects outward from the key (24, 24B-24G) and bites into the radial surface (31, 31B-31F) of the second tubular and transfers the decoupling force to the second tubular; a non-circular perimeter; an outer edge (30, 30B-30G) on a portion of the perimeter in contact with a radial surface (31, 31B-31F) of the second tubular when the key (24, 24B-24G) is in the locked position and when the key (24, 24B-24G) is in the unlocked position; and a lateral edge (25, 25C-25G, 42E, 58) on a portion of the perimeter that is in interfering contact with a side wall (18, 18B-18G, 20E, 22F) in the recess (16, 16A-16G) when the key (24, 24B-24G) is in the locked position, and so that when the first and second tubulars rotate in the decoupling direction a resistive force from the side wall (18, 18B-18G, 20E, 22F) to the lateral edge (25, 25C-25G, 42E, 58) transfers to the second tubular to rotationally couple the first and second tubulars; wherein the outer edge (30, 30B-30G) comprises at least one tooth that projects outward from the key (24, 24B-24G) and bites into the radial surface (31, 31B-31F) of the second tubular and transfers the decoupling force to the second tubular; wherein the recess (16, 16A-16G) is formed along a portion of a circumference of only the first tubular (12, 12A-12G), characterized in that the radial surface (31, 31B-31F) of the second tubular is normal with an axis (Ax) of the first tubular and the second tubular.