The KS9-40G is a low power X-band reflex klystron operating between 9.38 and 9.51 GHz. This exhibit was designed to be a local oscillator in radar receivers. We also have the KS9-40D, the difference will be the operating frequency. The basic operating parameters for this 40mW klystron are given in the advert referenced above.
The base and top cap are the greatest diameters on the central tube and reach 33 mm.
The International Octal base.
The output flange is 40 mm square. The screw is a matching device to make the impedance of the oscillator match the waveguide attached to it.
The thin glass tube envelope is 21 mm in diameter, and excluding the IO base pins is 70 mm tall.
References: Advert & The Radio Constructor. Type KS9-40G was first introduced in 1960.