On one side of the handle, you've got your blade that pivots around a joint. On the other side of the handle, there's a flat bar called a backspring. When you rotate the blade open, the blade's tang rotates against the backspring. The pressure of the backspring against the metal keeps the knife open.

What is the difference between a pocket knife and a pen knife?

is that pocketknife is a small knife whose blades or tools can fold in its handle, and thereby be safely stowed in one's pocket while penknife is a small pocketknife; a small knife with a blade which folds into the hand penknives often incorporate other tools such as corkscrews, and are generally smaller than ...

Why do they call it a pen knife?

Originally, penknives were used for thinning and pointing quills to prepare them for use as dip pens and, later, for repairing or re-pointing the nib. ... One popular (but incorrect) folk etymology makes an association between the size of a penknife and that of a small ballpoint pen.