Semi-finished silicone rubber in the extruded form or in the form of blocks, slabs, round bars, sheets and strips, tubes, gaskets, sealants, 0-rings, pipes and pipe couplings of silicone rubber for use in the manufacture of structural parts for the automotive, electronics, medical and construction industries; and packing materials, rubber packing of shipping containers, silicone rubber-joint sealant and insulation materials