Mezzotint rockers are used to create areas of rich black tone. Rock the tool across the plate in a criss-cross fashion to create lines of dots which eventually build up to create the tonal areas. More lines to the square inch create darker tones.
The rocker weight set attached to the rocker to help 'rock' the ground more efficiently with less effort.
Standard delivery charge is £4.99 if you are in the UK mainland.