The X-translation stage (x-stage for short) is used to move the disk horizontally so as to vary the wear track diameter of the test.

The movement of the disk is done by turning the knob located at the centre of the x-stage.

The black locking mechanism is to lock and prevent movement along the x-stage. If it is tilted left (as it is in the picture), it is locked. If it is tilted right, the x-stage can be adjusted.

The knob for the x-stage is currently faulty and cannot be turned by hand. However, a torque wrench can be used to turn it instead.