PURPOSE: To make media and a workpiece easily sortable by means of a magnet or the like, by forming an abrasive barreling the workpiece from the media with magnetism.

CONSTITUTION: For example, as media 1 for magnetic disc unit parts, each one is formed into conical form or triangular weight form by an abrasive grain- contained plastic. And, in order to make media 1 have magnetism, fine magnetic grains 2b are mixed in a fused media material 3 sealing a magnetic substance 2a in a media material 1a and they are coagulated and molded. The magnetism is given in a method of forming these media 1 themselves, coating a magnetic substance 2c on a surface of the media material 1a, by a magnetic material 2d or the like. Using suchlike media 1, after barreling a workpiece 4, if these media 1 are attracted by suction with a magnet or the like, these media 1 and the workpiece 4 are easily sortable.