This part of ISO 16232 describes the principles of extraction of contaminants from a component either by immersion in an ultrasonic bath or by applying ultrasonic vibrations directly via sonotrodes. It is preferably applied to small and medium sized components of various geometry of which both internal and/or external surfaces have to be examined (e.g. joint seals, gears, etc). It is also applicable to small parts to be analysed in batches. This method can be used on its own or in association with other methods of extraction described in the ISO 16232 series. NOTE 1 The suitability of this method for complex geometries – e.g. tiny bores or large cavities with small openings – is decided on a case by case basis. NOTE 2 Depending on the shape of the components, this method can be used also for batches containing multiple layers of components provided that there is no obstruction to the extraction of contaminants from the surface and their subsequent transfer into the test liquid. Small compact parts of large number are cleaned in a single layer. Unless otherwise specified, this part of ISO 16232 deals with particulate contamination only. It does not, therefore, cover appearance defects or contamination by liquid or gaseous materials. It covers the amount and the nature of residual particles resulting from manufacturing processes and from the environment.