A bicycle eccentric is a device whose main part is located inside the wheel axle. The main task is to fix the wheel in the seat.
How to choose an eccentric for a bike?
An eccentric is a part subject to mechanical shock, so it breaks over time. Any eccentric can be easily replaced. These elements are front and back. Otherwise, your choice can be based on lightness or reliability, that is, respectively, on aluminum or steel performance. You can always choose the handle of the latch lever that is convenient for you. Also note that different eccentrics are suitable for different types of wheels: 126, 130, 160 and 165 mm.