The Cossor RC is from their Point One series. This series of dull emitter valves took just 100 mA of filament current. The paper band is blue in colour to denote the RC type. The later catalogue Type designation was 210RC but this does not appear on the valve.
The paper band shows the filament voltage and current as well as the anode voltage to use.
The electrode system. At the top of the anode is a ceramic plug that holds the filament top support.
The balloon envelope is 42 mm in diameter and, excluding the B4 base pins, is 86 mm tall.
References: 1043. Type Point One - RC was first introduced in 1927.