A surgical robotic instrument comprising: a shaft; an end effector element; an articulation connecting the end effector element to the shaft, the articulation comprising: a first joint driveable by a first pair of driving elements, the first joint permitting the end effector element to rotate about a first axis transverse to a longitudinal axis of the shaft; a second joint driveable by a second pair of driving elements; a pulley arrangement around which the second pair of driving elements is constrained to move, the pulley arrangement comprising: a first set of pulleys rotatable about the first axis; and a second set of pulleys proximal to the first set of pulleys and comprising a first pulley rotatable about a second axis, and a second pulley rotatable about a third axis parallel to and offset from the second axis; and a clevis unit comprising two arms supporting the pulleys of the pulley arrangement, and a pulley guard extending from one of the arms for guarding one of the first and second pulleys.