A finline resonance isolator is an attractive solution to the construction of millimetre wave isolators, except for the fact that a large direct magnetic field is normally required for its operation. One way to overcome this drawback is to employ an hexagonal ferrite material with a large internal uniaxial anisotropy energy. Such devices are simple to fabricate and provide perhaps the most practical solution to the design of millimetre band isolators. The paper describes some experimental finline devices in WR 42 waveguide.