A covered sliding operator includes a body; a slot formed in the body; a spindle extending through the slot and which is slidable along the length of the slot; and a generally oval cover rotatably mounted on the spindle. The body has a first impinging wall and a second impinging wall. The cover is shaped such that: when the spindle is central in the slot, the cover completely covers the slot; moving the spindle towards the first end of the slot moves the cover against the first impinging wall and causes it to rotate in a first direction such that the slot remains completely covered by the cover; and moving the spindle towards the second end of the slot moves the cover against the second impinging wall and causes it to rotate in a second direction such that the slot remains completely covered by the cover.