for WR90 Waveguide.
X-band - frequency range to 8.2 ~ 12.4 GHz.
The probe (a fine piece of wire protruding from a 0.50 dia detector plug a little bit into the slot) is missing. This connects to a crystal detector in the plug. It is relatively easy to make one oneself, based on a 1N23 crystal diode.
After a slight clean-up of dust inside the WG, it could be a great base for precision measurements.
This unit is has been checked to be in working condition.