ISO 16232-4:2007 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 are 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. Unless otherwise specified, ISO 16232-4:2007 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.