A robotic surgical instrument, comprising: a shaft； an end effector element； an articulation at a distal end of the shaft for articulating the end effector element, the articulation comprising a first joint permitting the end effector to adopt a range of configurations relative to the longitudinal axis of the shaft, the first joint being driveable by a first pair of driving elements； and an instrument interface at a proximal end of the shaft, comprising: a chassis formed from the securement of a first chassis portion to a second chassis portion, wherein the first pair of driving elements are secured relative to the chassis, the chassis portions being configured to be secured together by sliding the chassis portions relative to each other in a longitudinal direction parallel to the longitudinal axis of the shaft.
