by the portions illustrated for example for milling standard 133 8 inch 34 cm casing the total length of the assembly is in the order of six meters it will also be apparent that as is commonplace in downhole tools the casing mill is made from several sections threaded together at the lower end of the casing mill there is a conventional stinger 10 having a conical end for entering the end of the casing to be milled the stinger may be essentially smooth or may include tungsten carbide or similar cutting material for milling occasional junk within the casing the outside surface of the stinger typically has a diameter only slightly smaller than the inside diameter of the casing for providing stabilization at the lower end of the casing mill excessive stabilization is avoided by providing a small degree of flexibility in the tubular body connecting the head of the stinger with the lower cutting portion of the casing mill next above the stinger is a coupling milling section 11 on which are mounted a plurality typically three of movable cutting blades 12 as described in greater detail hereinafter the movable blades are movable between a retracted position as illustrated in fig1 and an extended position as illustrated in fig2 above the coupling mill section is a mechanism 13 for switching the movable blades between the extended and retracted positions in the preferred embodiment as illustrated in fig3 and.