This exhibit is in wonderful condition. The top cap style shows this to be an early version. This battery RF pentode was produced in two versions, one on a B7 base and another on a B4 base.
The design application was RF amplification in broadcast radio receivers.
The picture above shows in detail the construction of the wire grids.
The further magnification demonstrates the way the grids were wound. The grid wire can be seen to be fitted into the support rod. In production the support rods were first notched by one cutting disc, the grid wire then was then wound into the notch and finally a blunt peening wheel would be used to close the metal over the grid wire and thus hold it in place.
The classic envelope is 36 mm in diameter and, excluding the B7 base pins, is 104 mm tall.
References: Data-sheet & 1043. Type 210SPT was first introduced in 1934.