The Citroen D21 uses the 1895 bulb across all listed model years (1969-1972) for both front and rear side marker positions.
The 1895 is an ANSI-standardized bulb type, meaning its specifications are governed by a defined North American standard used in the United States and Canada.
The 1895 belongs to the T5 form factor, which refers to a miniature wedge-base bulb with a tubular glass envelope roughly 5/8 of an inch wide.
The wedge base design means the 1895 is held in its socket by the glass envelope itself rather than by a separate metal base, which is a common trait of low-wattage indicator and marker bulbs.
The 1895 operates at 12 volts, consistent with the standard electrical system voltage found in most conventional passenger vehicles of this era.
At 0.9 watts, the 1895 draws very low current, which is typical for side marker applications where continuous illumination is required without significant load on the vehicle's electrical system.
The front and rear side marker positions on the D21 share the same bulb specification across all listed years, indicating full interchangeability between those two positions.