Abstract: A lockable dip stick assembly for an oil filling spout comprises an elastomeric stopper disposed between an outer compression cap and an inner compression plate which carries a dip stick. A stud extends coaxially through the cap and stopper and threadably engages the compression plate. A bell housing supported for rotation on the outer end of the stud contains a key operated lock cylinder which has a bolt radially movable between uncoupled and coupled positions corresponding, respectively, to locked and unlocked positions of the lock cylinder. In a coupled position the bolt is connected in driving relation to a drive cup mounted in fixed position on the outer end of the stud and enclosed within the housing. Rotation of the key to and beyond an unlocked position causes rotation of the stud relative to the compression plate.