the shower base of a shower head consists of a rigid perforated plate , which has a number of holes . set inside each of the holes in the perforated plate is a hose - type jet insert made of a flexible material which , owing to its material properties , can be automatically flexed to dislodge limescale deposits . the shower base is sealed against the rest of the shower head , in particular against its housing by means of one or more seals . this / these seal is / are made of the same material as the jet inserts and is / are manufactured jointly with these , for preference connected in one piece . in this way , it is not necessary for the seals to be manufactured , kept in store and assembled separately .