The RD4 is a directly heated dull emitter battery triode. The low current indicates an oxide coated filament. Triotron state that it is both general purpose and designed for IF amplification in superhet receivers.
The Lettering is etched into the glass. Triotron Radio is an Austrian company. The silver gettering obscures the electrodes.
The base pins are brass split pins of two part construction. The pin is screwed into the base that is fixed into the composition base.
The flattened rectangular anode is mounted at an angle within the bulb.
The balloon envelope is 45 mm in diameter, and excluding the B4 base pins is 89 mm tall.
References: Data-sheet, 4045 & 1043. Type RD4 was first introduced in 1928.