What do you make of this?

[Nick]

First British X band reflex klystron CV87. The double thread coarse & fine tuning mechanism was difficult to manufacture and the wide tuning range largely unnecessary for actual use outside of bench tests so comparatively few were made. The same tube and resonator structure was fitted with a simpler tuner for a smaller tuning range as the CV129, Cv223, Cv224 (different tuning ranges) and were used in early X band radar

https://www.radiomuseum.org/tubes/tube_cv87.html