CMS Magnetics rare earth magnets are made of neodymium, which makes them up to 12 times stronger than ceramic magnets of equivalent size. Neodymium magnets are extremely versatile because of their strength and can be used in a wide variety of applications ranging from holding things onto your fridge to the most demanding industrial applications. This product measures 0.59" (thick) by 2.36" (diameter). Round base or 'cup' magnets offer such a strong holding force due to their unique design, which concentrates both the North and South poles on the flat side. Additionally, the steel cup enclosing provides protection to the strong Neodymium magnet inside. The countersink is made for a size #18 flathead screw, and is designed to be completely flush on flat surfaces. This magnetic blend is patent licensed and made under the ISO 9001 quality control systems. They are plated in a nickel-copper-nickel coating for a shiny corrosion-resistant finish. The north and south poles are on opposite sides. The pull force of each individual magnet is 249 lbs. PLEASE NOTE: Neodymium magnets are brittle and will chip or shatter if they are allowed to collide with each other or onto a magnetic surface. Keep away from pacemakers and other objects that are sensitive to magnetic fields. If magnets are swallowed, they can join inside the digestive tract and cause extreme injury or even death.