The 17Z3 is an efficiency diode for television line scan and the design dates to the early 1950s. This was a popular design and was made by many companies under various Type designations.
The rectifier is specified as having a peak inverse voltage rating of 4,500 Volts, and a peak current rating of 450 mA.
The inner faces of the anode are seen as the metal is folded outwards and by doing so, to increase surface area for heat dispersal.
The anode has the two sides stitched together.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 73 mm tall.
References: Datasheet, 3002 & 1040.