The 'Onoto' name was first used, by the De La Rue pen company in 1905 after the plunger filling system was patented in the same year. This 'Patent Self filling Pen' was the first pen to be made using the Onoto name.
The pen was made in two versions the 'O', this pen, and the longer 'N'. The 'O' pen was particularly popular with the military as it would fit into a uniform breast pocket and allow the flap to be closed, a requirement for many occasions. It was still sold in far fewer numbers than the longer pen and is consequently now a good deal harder to find.
At 12 cm. when capped, the pen grows to a very respectable 15Cm. when the cap is posted on the barrel for use. The cap posts securely on the filler button at the end of the barrel, the pen was designed to be used in the posted configuration.
The condition of the pen is remarkable. It is constructed in black chased hard rubber (BCHR) with a clear engine turned 'chevron' pattern on the barrel and a plain cap. The barrel imprint is crisp and clear, it reads: