For integrated shifting units on the steering wheel see paddle shifter. 

Shifters, in sim racing terms, are external units that simulate the shifters and gearboxes used in real vehicles. There are three construction types of shifters: classic H pattern shifters simulating manual transmissions, sequential shifters, and hybrid units that combine both, an H pattern as well as a sequential mode, due to a mechanical lock.

Normally, all three units use potentiometers to detect the shifting processes. Shift travel is kept short on almost all models to achieve a sporty feeling.

As with the pedals, external shifting units need to have a sturdy mount, as high-quality shifters are usually made of metal and carry a high dead weight. In addition, sequential units have spring mechanisms that return the shift rod to its original position, which also requires a lot of force to be applied to engage the gears.

 

(Symbol image: Fanatec Clubsport Shifter SQ V1.5)