The GRD 7 is a guard ring diode for educational purposes or as a saturated diode for use in stabilised AC supplies. The data-sheet is dated 1961 and issue 4 so this valve probably dates to the late 1950's.
The PDF makes very good reading.
The anode is the centre section with the guard rings above and below. These electrodes are made of non-magnetic material.
The guard rings are strapped together by the support rods.
The large hole in the top mica is to allow observation of the tungsten filament when heated. This allows the estimation of its temperature by optical methods.
The tungsten filament is 0.125 mm in diameter. The anode internal diameter is 6.5 mm. The effective filament length, within the anode, is 14.5 mm.
The pinch. The tungsten filament passes through the centre of the anode and guard ring.
The cylindrical cavity of both guard ring and anode is made by pressing and folding the thin sheet material.
The wide glass tube envelope is 29 mm in diameter, and excluding the IO base pins is 92 mm tall.
Reference: Data-sheet. Type GRD7 was first introduced in 1959.