These neodymium ring magnets are part of our 19mm (0.75") diameter range. They are used in many everyday appliances such as vacuum cleaners plus motors, generators, rotor shafts and more. They can even be used to demonstrate intriguing 'eddy currents' using a 9mm (0.31") copper pipe. Simply slide the ring over the pipe and let it slide down its length and watch it slowly descend as the eddy currents produced create a damping effect. Compare this with an unmagnetized ring of the same dimension by repeating and watch as the unmagnetized ring slides down the pipe in an instant. A great way to bring magnets to life in the classroom.