a milling tool and the slots facilitate the break up of the cone and reduce the likelihood of such smearing the reaming members 36 are formed of an aggressive cutting material such as tungsten carbide blocks welded to the leading end of the body to define reaming blades each blade 36 comprises a leading pilot portion 63 which defines a taper extending rearwardly and helically from the nose cone 34 rearwardly of each pilot portion 63 is a larger diameter reaming portion 62 with tapering leading and trailing ends 64 66 each reaming portion being spaced from but helically aligned with the respective pilot portion 63 it should be noted that as the leading end of each blade 36 overlaps longitudinally the trailing end of an adjacent blade 36 the blades 36 collectively provide 360 u00b0 coverage of the body like the first described embodiment fluid outlet ports 68 which communicate with the interior of the body are provided between the blades 36 in this embodiment it will be noted that adjacent ports 68 are longitudinally offset to minimise weakening of the body 32 the centraliser 38 is located at the longitudinal centre of the shoe 30 and comprises a bushing 70 defining five blades 72 although the number of blades may be varied as desired the bushing 70 is rotatable on the body and is located between a body shoulder 74 and a lock ring 76 in use two fluid conduits not shown carry fluid from the body interior to lubricate the bearing surfaces between the bushing 70 and the body 32 the blades 72 each comprise a main helical portion 78 and axial.