pins instead of the fingers the base disc of the pot is made by compression moulding suitable acid resistant materials or by injection moulding of glass filled thermoplastic materials like nylon acetol polycarbonate or polypropylene the base disc may have a layer of thin smooth and acid resistant plastic film bonded to the top with a suitable adhesive which could be removed by solvent removal of the said adhesive the plastic film layer is of polyester polypropylene polyethelene ptfe or such materials the adhesive used may be a hot salt thermoplastic or a pressure sensitives elastomeric or any other polymeric adhesive like epoxides the base disc also has a disposable bush at the centre which is accurately concentric to the spigot and the same gets its accurate location by being fitted into a close fitting bush which is integral with the base disc the integral bush is moulded as an insert and fine bored accurately concentric with respect to the spigot and is fitted into a moulded central cavity by adhesive bonding and then fine bored the disposable bush may be made of metallic materials typically phospor bronze or of low friction non metallic materials typically ptfe the integral bush may be made of metallic materials typically aluminium or of non metallic materials typically cloth laminated phenolin the external surface of the barrel as well as the internal surface are both made concentric to each other and to the spigot as also the axis of rotation the surface finish of the barrel in new condition would be of mirror finish.