This is a radial magnetized isotropic ferrite ring with grooves on one side of the magnet so that it can be used in a wider range of applications, the actual dimensions of the magnet are 17.2mm OD, 6mm hole, 7mm thickness, we have stock to supply, if you are interested in this product you can send an inquiry to us for price.
Isotropic ferrite magnets with holes and grooves with pole distribution and sample picture presentation
Looks about the same size slightly larger magnet;
Ferrite ring magnet with one-side notch groove 30 x 12 x 5 mm