Most commercial mass spectrometers are intended to select ions by focusing them in one direction by means of electromagnets. However, double focusing is demanded in applications where the pole‐pieces gap is too tight. A mass spectrometer has been planned and built to focus an ion beam in the radial and axial directions using permanent magnets in a circuit with nonparallel pole pieces. Consequently, the magnetic circuit in the spectrometer does not require anyexvacuoconnection for its functioning, and the size can be controlled by just choosing the appropriate magnets. The measurements of the magnetic field configuration show good agreement with the theoretical prediction in the gap radial region where the H−species from a H−surface production experiment are deflected. The description of the criteria followed in the design and construction of the mass spectrometer is the main object of this report. ©1995 American Institute of Physics.