The Point One HF & Det from Cossor was so named to showcase their low consumption valves. Later in 1927 Cossor introduced their unified ranges and the Point One HF & Det was renamed as the x10HL where the x is the filament voltage and could take the value 2, 4 or 6 the 01 is the current. In this exhibit the filament is the four Volt version. The HF & Det was identified by the red paper band.
The valve was designed for broadcast radio reception and would be used for the signal stage(s) and the detector. The Point One LF would provide audio amplification.
The filament rating and maximum anode voltage.
The shape of the anode and within can be seen in addition to the grid the oxide coated filament and the three filament supports.
The balloon envelope is 39 mm in diameter, and excluding the B4 base pins is 82 mm tall.
References: 1043 & 1040. Type Point One - HF & Det was first introduced in 1927.