Abstract: The apparatus includes a scanning system for scanning a projected image of an axially symmetric component's profile in a plurality of lines of scan, each line of scan being transverse to the axis of symmetry of the components profile and having a predetermined spatial relationship with respect to a neighboring line of scan. The scanning system may include a linear or two dimensional array of image detectors and the system produces electrical signals representative of the extent of the image of the component's profile along each line of scan for processing by a computer which uses these signals to calculate at least one of the parameters of length, breadth and curvature of the axis of at least a portion of the component and determines whether the parameter lies within a predetermined range.