sectional area of the inner surface 28 of the sleeve 22 the outer surface 30 of the sleeve 22 is substantially circular but includes four indents or grooves 32 a u2013 d the grooves 32 a u2013 d ensure that fluid can flow past the tool 10 at all times mounted on the sleeve 22 are four moveable pads 34 a u2013 d each pad 34 a u2013 d can move radially away from the body 12 to a point at which overhangs 36 on the sleeve and 38 on the pad connect it will be appreciated that although only indicated at one overhang the overhangs 36 38 exist around each of the moveable pads this is clearly evident in fig1 where the pads are seen to be circular the outer surface 40 of each pad is an abrasive surface to provide better contact to the wall of the tubing not shown to prevent the circular pads 34 a u2013 d from spinning they are both held by the overhangs 36 38 and located on an offset grub screw 42 and a cover plug 44 each grub screw 42 is attached to the body 12 and the pads 34 a u2013 d can slide along the outer edge of the grub screw 42 and cover plug 44 to assist in this the cover plug 44 is made of ptfe within the tubular body are four radial ports 46 which provide fluid contact to the sleeve 22 where each radial port 46 meets the sleeve 22 there is a passage 48 on the sleeve 22 which allows fluid to travel to a chamber 50 located between the overhangs 36 38 within the chamber 50 is located a spring 52 which preferentially holds.