This HL210 has straight cuts in the base pins and just the HL210 etched into the glass near the base. The structure matches the Mazda product.
The HL210 is a general purpose battery triode with a two volt filament.
The gettering is to one side only and the construction can be seen. There is a small mica sheet at the top but insulated support is also provided by the glass bead fused to the central rod.
In this image it can be seen that the glass bead holds struts that fix to the grid supports at the top of the valve. The central rod passing through the bead supports the filament tension spring. The filament is a single hairpin and has a white oxide coating.
Another view showing how small the electrode assembly is in relation to the balloon envelope.
The balloon envelope is 45 mm in diameter and, excluding the B4 base pins, is 89 mm tall.
References: Data-sheet. Type HL210 was first introduced in 1929.