The 10F1 is an early all glass screened amplifier pentode. The high impedance suggests applications with tuned circuits as anode loads, such as RF, or more likely due to the high gain, IF amplification in superhet radio, television or radar receivers.
The pins are located equi-spaced around the base circle and the metal skirt and spigot aid location. The pins are short and hard as was the case with some early all glass designs.
Through the holes in the outer screen can be seen the wire grids and where the view is blocked there are small vertical anode plates.
The rectangular cathode tube. The copper supports of the control grid have a small radiator fitted.
The thin glass tube envelope is 20 mm in diameter and, excluding the B8A base pins, is 53 mm tall.
References: 3002 & 1040. Type 10F1 was first introduced in 1948.