Methods of assembling a vertebral anchor to a body shaped to receive a longitudinal member. Microwave input power is efficiently coupled with an ionizing gas without using a dielectric microwave window and without developing a throat plasma by providing a ferromagnetic cylindrical chamber wall with a conical end narrowing to an axial entrance hole for microwaves supplied on-axis from an open-ended waveguide. The injection sleeve applies a transverse contact pressure when it engages the mold portions. The user is able to input data via any appropriate input mechanism, and receive data on any suitable output mechanism.