This double diode appears to have a cylindrical anode, but in fact the visible cylinder is a screen strapped internally to the cathode. Within the screen are two small anodes mounted vertically around the cathode.
The bright screen with stitched side flanges.
The heater has four insulated strands within the cathode tube.
The classic envelope is 38 mm in diameter and, excluding the B5 base pins, is 90 mm tall.
References: Data-sheet & 1043. Type 10D1 was first introduced in 1936. See also 1936 adverts.