tip elements 52 becomes narrower in a tapered fashion in the direction of the leading end 34 in order to even more clearly understand the construction and functioning of barrel lock sleeve 18 its operation will now be described in detail once the glass window has been removed from door aperture 16 sleeve 18 is snap mounted within the door aperture by inserting the tip portion 36 into the door aperture the relatively small diameter tip portion 36 easily fits into and passes through door aperture 16 as the sleeve is pushed axially through the aperture the maximum outside diameter portion 44 of locking ball retaining portion 38 contacts the door aperture continued axial pressure on the sleeve causes the locking ball retaining portion to momentarily resiliently reduce in diameter because of the reduction in width of slots 50 until the locking ball retaining portion 38 passes entirely through door aperture 16 then both the tip portion and the locking ball retaining portion are positioned on the inside of the meter box front door 12 in this position neck portion 40 seats snugly within the door aperture 16 and the shoulder portion 42 abuts against the outside surface of the door 12 forming a stop by which barrel lock sleeve 18 is prevented from further axial movement towards the meter box interior after the locking ball retaining portion has cleared the door aperture its maximum outside diameter portion 44 snaps back and regains its original uncompressed diameter which is larger than the door aperture diameter thus the barrel lock sleeve is snugly snap mounted within the door aperture in order to lock the sleeve within the door aperture a conventional barrel lock 20 is inserted.