Knowledge Base

A cassette is a series of rings that slide onto a body on the rear hub and held in place by a lock ring. A freewheel is a one-piece unit that has the body built-in and threads onto the hub. Most cassettes have 8 rings or more, whereas freewheels usually contain 8 or less. Many low end or older bikes will use a freewheel system. A cassette requires tools for fitting, a freewheel doesn't.

A quick search on YouTube will show a simple visual demonstration around the difference between the two.