Lab
Grind scale.
Click a method and see how fine and why. The ranges and comparisons are a rough guide, not a standard: every grinder has its own scale, so watch the coffee, not the number.
How a grinder works
Blades, burrs and clicks.
Blades
They chop instead of grinding: coarse and fine particles together, with no repeatable result. They do not work for espresso.
Conical burrs
As a rule they spin more slowly and are often quieter. They tend towards slightly more fines and more body.
Flat burrs
As a rule they give a more uniform particle and a cleaner taste. That is a tendency, not a rule.
Stepless
Continuous adjustment, so small corrections for espresso are easier.
The best machine cannot fix a poor grind. So when choosing equipment, sort out the grinder first. The whole story is in the guide Grinding and grinders.