From Typewriter Wiki

Typebars are metal arms with typeslugs on their ends, responsible for striking the ribbon and paper when typing to print. On most typewriters, each typebar corresponds to one key on a typewriter. All of the typebars collectively are called a type basket. On most machines, the typebars have a pivot point in the segment. They stay in a resting position, laying on a piece of felt or similar typebar rest, until the corresponding key has been pressed.

Although this mechanism is most commonly used, not all typewriters use typebars.

Commonly occurring problems

A sticky segment is a common problem when fixing a machine that has not been used for a while. Flushing it with mineral spirits or isopropyl alcohol and using a toothbrush to get in the slots is recommended. Afterwards, it is best to use compressed air to get all solvent and gunk out. Note that when working with mineral spirits or other paint thinners, they should be kept away from all painted surfaces, as they will eat through the paintjob and damage it.

Another common problem are bent typebars. It is important to be careful when fixing those, because there is a risk of the bar breaking off. It's advised to carefully bend the typebar back into its proper position using fingers or pliers. There also are typewriter-specific tools for the job, but those are hard to come by.

It's also a common occurrence for a typewriter to not be "soundproofed". This means that the typebar rest is not covered by anything, so when a typebar falls back onto it, there is a sound of metal hitting metal. This makes typing much louder. Most typewriters were soundproofed when manufactured, with a piece of leather or felt, attached to the typebar rest, but those have often fallen off at some point. To make typing quieter, it is recommended to resoundproof the machine. A strip of felt/leather can easily be glued to it. It is important that that strip is not too thick - if it raises the resting level of the typebars too much, it will cause them to jam together.