Question: are there different size cassettes?
Answer: Sprockets vary in size according to the number of teeth they have. A cassette may therefore be sized as 11-32t. ... The closer the two figures are together, the less pronounced the difference between gears (e.g. an 11-21t cassette is referred to as having a 'narrow' gear range, and an 11-34t as having a 'wide' gear range).