The VT-266 is a half wave rectifier designed for pulse applications. The peak current can be up to 2,500 mA and the design allows for a high peak inverse voltage of 5,500 Volts. Such demands would be placed on a rectifier that was required to recharge a capacitor stack after a pulse discharge such as that found in Radar transmitters.
Faintly etched into the envelope in the main picture can be seen the commercial code of 1616.
The anode appears to be made of graphite. The ceramic insulators are there to allow for the high voltages.
The oxide coated filament is a pair of inverted V ribbons held in tensioning springs. The top mica is an interference fit to the top of the envelope.
The lower ceramic support and the base of the filament. The un-coated filament shows that it is made of gauze. A close inspection of the top of the filament also reveals the gauze under the coating.
The envelope is 51 mm in diameter, and excluding the UX4 base pins is 151 mm tall.
References: Datasheet. Type VT-266 was first introduced in 1942.