How to distinguish Freewheel and Cassette

The differences between cassette flywheel and rotary flywheel are: different disassembly, different structure and different using vehicles.

1、The connection between flywheel and hub of cassette flywheel is spline tower base and locking piece, and the teeth piece can be disassembled. The tooth discs of cassette flywheel are stuck together one by one, and there is a tower base in the middle, so you can set them up one by one. 9 speed is composed of 9 flywheels, if there is a separate flywheel is bad, it can be replaced separately.
2、The connection between flywheel and hub of spin flywheel is threaded, and the teeth cannot be disassembled. Spin flywheel is one piece, if there is a tooth is bad to replace all.

1、The ratchet structure of spin flywheel is inside the flywheel, not on the hub, which is the same structure of traditional bicycle single speed flywheel.
2、The ratchet structure of cassette flywheel is inside the tower base of the hub, and the flywheel is only composed of several teeth, without any complicated internal structure.

1、Spin flywheel is mostly used in single speed bikes, climbing bikes, old shifting sports bikes and low end entry level sports bikes, such as 6 speed and 7 speed bikes.
2、The cassette flywheel is more stable, lighter and can make the smallest tooth piece smaller, so the modern sport bikes in the middle and high-end level mostly use cassette flywheel.

It is so named because it is mounted directly on the tower base of the rear hub (i.e. rear axle) and is pressed with a threaded flywheel top cover. The ratchet structure of the cassette flywheel (that is, the source of the "clicking" sound when the rear wheel is idling without any pedaling) is inside the hub's tower base, and the flywheel is composed of only a few teeth, without any complicated internal structure.
There are two types of cassette flywheel mounts: Japanese (Shimano specification) and Italian (Campagnolo specification), of which Japanese is the majority and Italian is more common on road bikes with Campagnolo transmission/shift kits.

The flywheel is screwed directly onto the threads of the spinning hub through the threads that come with the flywheel. The ratchet structure of a spin flywheel is inside the flywheel, not on the hub, as is the case with the single-speed flywheel on a traditional bike.
Because of their more stable construction, lighter weight, and ability to make the smallest teeth smaller, modern sport bikes in the mid- to high-end segment tend to use cassette flywheels, while spin flywheels are found on single-speed bikes, climbers (with the spin flywheel forward on the teeth), older shifting sport bikes, and lower-end entry-level sport bikes. Currently, spin flywheels are available with up to 10 teeth, i.e. 10 speeds, while cassette flywheels are available in 12 speeds.