[Malcolm]

For cleaning the inside of the plate. There are four hex head screws, one in the centre with a raised dome head and three in a triangular formation. There is a gold band behind the ring that secures the plate. The inside of the front black ring is threaded, with a smaller ring insert which has two holes,one on each side of the ring. Is this ring the part that needs to be removed to get at the inside of the plate? The primary is clean, only what appears to be a few mould spots on the inside of the front plate.