Abstract: In a device for testing the rim around the apertures of bottles for flaws there is a rotor which has an optic fiber bundle for transmitting light to the rim or sealing surface of the bottle and another fiberoptic bundle for receiving light reflected or scattered by the surface that is to be sealed with a crown cap. The optical axes of the light transmitter and receiver are arranged in a common scanning plane which is substantially perpendicular to the plane of the aperture or rim and intersects the plane tangentially to the sealing surface. The optical axes are inclined by an acute angle, alpha, with respect to the plane of the aperture or rim. The light transmitter and receiver optical bundles have lenses at their ends for, respectively, projecting a light beam through the aperture plane and for receiving light reflected or scattered therefrom. One end of the light conductor or transmitter is coupled to a light source. One end of the light receiver is coupled to a photosensitive device.