Abstract: A locking member is formed with a circular plate and an upstanding rim and is adapted to be pivoted between locked and unlocked positions beneath the head of an orbital sander. When in its locked position, the locking member holds the spindle of the sander against turning and permits the sanding pad to be unscrewed from the spindle. The plate of the locking member includes a dimple which engages the head and causes the locking member to rotate concentrically with the head when the locking member is in its normal, unlocked position. The rim of the locking member performs a fail-safe holding function in the event the dimple fails and also prevents the locking member from being improperly installed in an upside down position.