The 2G is a Barretter or current stabiliser. Iron wire in a hydrogen atmosphere forms the active element. When inserted in series with a 100 mA heater chain it can maintain the heater current sensibly constant for variations in the mains voltage between 5 and 40 Volts.
Baretters cannot be connected directly across a voltage source.
Inside the envelope were two separate wire loops. One loop connected to pins 1 and 4 and the other to pins 2 and 3. This exhibit has been subjected to a sharp knock that has broken the central glass support and parted the wire loops.
The Paxolin base fixed by a bolt.
A closer view of the damage. The supports at the top of the glass rod are empty and the wire coils are broken.
The wide glass tube envelope is 25 mm in diameter, and excluding the base pins is 82 mm tall.