Bearings are located on the axle, pedal, and crank. The crank bearing is usually sealed. This is where the down tube, seat tube and chainstay join and houses the crank and crankset. It houses either an adjustable bearing or a cartridge bearing. They come in a variety of shapes and materials.
Most levers are now adjustable and come in different lengths.
Two-fingered levers are now most popular and quite effective. A fine tuning can be done at the handlebar barrel adjuster. They can be adjusted, and sometimes removing the wheel will cause the spring to come loose. They run thru cable guides. Chain Features here are proper length, maintenance, and quality.