This magnet is hollow cylindrical magnet with two grooves on the two-sides of cylindrical surface. The material is sintered ferrite, The specific size is 12mm diameter, 20mm in thickness and the thickness of the middle concave is only 6 thick, if you wanna the neodymium material, we also can do it, for example neodymium cylinder magnet with hole and two-sides groove.
The sample diaplay of ferrite cylinder magnets with two-sides groove 12mm dia x 20mm: