Lockable contact plate

A contact plate comprising

• (a) a circular dish supported on a circular base, said dish having a bottom plate and a bottom cylindrical side wall, and
• (b) a circular lid having a top plate and a top cylindrical side wall, said lid sized so as to fit over the bottom cylindrical side wall of said dish
• wherein said base and said lid are provided with locking means for securing said base and said lid in locking engagement, said locking means comprising at least two pairs of locking members, each of said pairs of locking members comprising (i) a radial sheath having an entry, and (ii) an elongate radial tab sized and shaped so as to be slidably engagable with said radial sheath wherein said radial tab has at least one protrusion and said radial sheath has at least one indent, with said protrusion and said indent being sized and located so as matingly engage each other;
• and wherein said at least one protrusion is proximal to the entry of said sheath and said at least one indent is distal to the entry of said sheath;
• and wherein said sheath has a closed end distal to said entry.