16454A is designed for accurate permeability measurements of toroidal-shaped magnetic materials. Since the construction of this fixture creates one turn around the toroid (with no magnetic flux leakage), the need of winding a wire around the toroid is unnecessary. Complex permeability is calculated from the inductance with and without the toroid. When the E4991A/4291B with option 002 is used as the measurement instrument, direct readouts of complex permeability are possible. In addition, it is furnished with a small and a large fixture to adapt to a wide range of sizes.