996,832. Honing. J. SUNNEN. June 27, 1963 [Sept. 17, 1962], No. 25593/63. Heading B3D. A honing mandrel comprises a tubular member adapted to be moved into a bore to be honed, an opening formed through one side of said member, a single abrasive assembly positioned in said opening, said assembly having an outer abrasive portion and an inner backing portion with a longitudinally tapered inner surface, and adjustment means movable longitudinally in said tubular member and engageable with said tapered inner surface for moving said abrasive assembly radially in said opening, said adjustment means and said tubular member having co-operating relatively movable means to prevent relative rotational movement therebetween. A honing mandrel for bores having a diameter of one-tenth of an inch or less comprises a tubular holder 12 and a case-hardened tubular barrel 14. A rectangular opening 22 formed, e.g. by electrical discharge machining, in the barrel 14 receives a stone assembly comprising an abrasive element 30 attached to a stone holder 32 having a tapered inner surface 34 mating with a tapered surface 44 on the end of a rod 40 slidable in the barrel 14 and extending from a portion 38 slidable in the holder 12. The portion 38 has a stud 46 received in alongitudinal slot 48 in the holder 12. The holder 12 is of a size to fit existing honing machines and the portion 38 has means co-operating with adjustment means on the machine to control its axial position in the mandrel, and hence the radial adjustment of the stone assembly. The barrel 14, except for the portion which fits into the holder 12 and in the area of the opening 22, is cut away on the side substantially opposite to the opening 22. The cut-away 26 is not symmetrically opposite the opening 22 but is offset, e.g. through 7 degrees to the side indicated in Fig. 4 for a mandrel designed to rotate counterclockwise. The cylindrical portion of the barrel 14 in the area of the opening 22 forms a shoe 28 which engages a bore during honing to provide support and backing for the abrasive member. In a modification, Fig. 10, the stone holder 32a has a longitudinal projection 33a to prevent the stone assembly from flying out of the barrel 14. In another modification, Fig. 11, one side of the opening 22b has a projection 50b a few thousandths of an inch thick, thus reducing the area of the opening that has to be made to exacting tolerances. A thick projection may be used, a mating notch being provided in the stone assembly. In another modification, Fig. 12, one side of the barrel 14b has a flat 54, formed at an angle approximately 7 degrees to a centreline through the stone assembly, to facilitate circulation of lubricant in the bore during honing. A second parallel flat may be provided on the opposite side of the barrel.