The 3180 is a neon tuning indicator. Within the thin glass tube is a wire rod and a pair of circular electrodes. To function as a tuning indicator it produced a column of glowing plasma that changed length by virtue of a changing control potential.
The data-sheet does not make clear the difference between the 3180 and the 3184.
The base is a small bayonet fitting where the case is the third connection. The pinch and two annular electrodes are on the right. Note the cracked insulation on the attached wires.
A closer view of the two ring electrodes.
Looking along the glass tube the central electrode can be seen to be supported at one end only.
A close-up of the top ring electrode with the welded connection on the right.
The thin glass tube envelope is 13 mm in diameter and, excluding the base pins, is 93 mm tall.
References: Datasheet & 4010. Type 3180 was first introduced in 1934.