Abstract: An apparatus and corresponding method for machining at least one spline in an aeronautical component. The apparatus comprises a holder defining an axial direction about which the holder is moveable, and a cutting insert attachable to the holder. The apparatus further comprises a coupling for attaching the cutting insert to the holder about a second direction that is perpendicular to the axial direction of the holder. The holder may comprise a first alignment feature for orientating the cutting insert at a single orientation with respect to the holder. The cutting insert may comprise at least one cutting tooth, wherein each cutting tooth comprises a cutting edge. The cutting insert may comprise a first datum surface which is spaced from each cutting edge by a respective predetermined spacing.