At the National Institute of Standards and Technology a new watt balance, NIST-4, is currently being designed. This apparatus will be used to realize the base unit of mass after the redefinition of the SI has taken effect. As a realization device, NIST-4 shall be easy to use and of low maintenance. Guided by these requirements we decided to use a permanent magnet sys-tem to generate the magnetic flux for NIST-4. A brief overview of the permanent magnet system is given.