Flex nib

Due to its non-rigid structure, a flex nib allows a writer to control line width by adjusting the pressure of the pen on paper.

Increased pressure will cause the two tines of the nib to separate slightly, allowing more ink to flow onto the page.

They were typically offered as an option on a manufacturer's pens so that the same model could come with a standard rigid nib or flex.

Flex nibs require considerable skill to make and were typically manufactured with a 14k gold alloy.

This alloy gave the nib enough flexibility to support the classic Spencerian or Copperplate writing styles.

Therefore, downward pressure must be carefully controlled to avoid damaging the nib while lateral force increases or decreases depending on the separation of the tines.

This is due, in part, to the decrease in popularity of script styles using flex pens during the early 20th century.

Another factor leading to their decrease in use was the level of skill required to ensure no damage to the nib's tines.