a single - block central plunger is manufactured , which is particularly suited for the production of boxes made of plastic material for electric accumulators . the mould includes a mobile plate supporting some lateral cores and a fixed plate supporting a fixed central plunger , wherein the mobile plate moves co - axially in relation to the fixed plate by sliding on some guiding columns . the fixed central plunger supported by the fixed plate is made from a single block and its cores are obtained from the same block , as well as its box angle - plate , preferably by machining them with wire cutting spark erosion tool machines .