This exhibit has no Type designation on the envelope. It is a barretter and M-OV made a B4 based barretter in 1934 the 251 which is what this was thought to be, however, at a few volts across pins 3 and 4 the wire heated and fused too fast to shut off the power. So it is possible that this was a very low current device for stabilising oscillators.
The wire is clamped to the supports.
The faint etched lettering on the envelope.
The wide glass tube envelope is 33 mm in diameter, and excluding the B4 base pins is 100 mm tall.
