Abstract: An apparatus for use in coating a selected area of a surface of a body, such as a flat disc type body, includes a support member having a recess in one side which is adapted to receive the body and an opening through the bottom of the recess which is smaller than the recess. A cup-shaped cover plate is adapted to fit into the recess in the support member. The cover plate has a bottom which is adapted to engage the body and hold it firmly against the bottom of the recess with the surface of the body to be coated being exposed through the opening in the support member. A mask of a magnetic material is adapted to fit in the opening in the support member against the surface of the body. A permanent magnet is adapted to be seated against the bottom of the cover member and attract the mask to hold the mask against the surface of the body.