The Parker 21 Mk.1 is markedly different from later versions in that it has a larger opening in the hood exposing a distinctive rounded feed and has a 'ridge' clip. It is quite a rare pen.
This is a particularly fine example. Finished in Blue, the barrel bears a legible date code for the first quarter of 1955, a very late pen for a Mk.1.
The 'Octanium' nib is quite exceptional, it has good ink flow writes with a very smooth, medium line.
The Parker 21 is an extremely good choice as an unusual and dependable every day writer and is often favoured rather than the much more expensive Parker 51 to which it bears a close, if superficial resemblance. It is an excellent pen in its own right and a Mk.1 in such excellent condition is hard to find.