Abstract: Mechanical thru-tubing centralizers 12, 14 positioned along a work string WS centralize a tool such as an abrasive cutter AC within a large diameter casing C after passing through a small diameter tubing T. The centralizer 12 includes a body 60 having a throughbore 62 for transmitting fluid through the centralizer to the abrasive cutter AC. The centralizer 12 also includes arm support sleeves 44, 46 each movable axially between a set position and a retracted position in response to the biasing forces of coil springs 40, 42. The springs 40, 42 bias the arm support sleeves, such that a plurality of circumferentially spaced upper arms 48 and a corresponding plurality of circumferentially spaced lower arms 50 are each inclined with respect to the centralizer body 60. Pads 52 pivotally connected to the upper and lower arms are substantially moved radially outward with respect to the centralizer body and thus engage the inner diameter of the casing string C to maintain the centralizer in a set position.