D 12mm x H 3mm with 4mm Hole | it is Ferrite Magnets,not strong magnets,Grade 5, It is highly stablility udner difficultal environment | Countless ways to re-organize and simplify your life, There's so many ways to use magnets | Durability - magnets have high resistance to demagnetization, corrosion and oxidation | Great for all Home, Office, Craft, Science Projects and Product Manufacturing application