This is a disk magnet which is single face with groove, the material is sintered ferrite, ferrite has become a widely used non-metallic magnetic material in the field of high frequency and weak current. The specific size is 14mm in diameter, 8mm in thickness, the groove (generally) is 1mm deep. The working temperature is batter than neodymium magnet and is less than 250℃.
The measurment of 14mm x 8mm sintered ferrite disc magnets with one-side groove: