Worm gear adjustment

A high-resolution grind-adjustment mechanism using a worm-and-gear drive — found on precision grinders like the Weber Key and some premium hand grinders.

Why it matters — Worm-gear adjustment gives much finer control per rotation than collar-thread systems. One full turn might only change the burr gap by 0.05 mm, where a threaded collar might move it 0.5 mm. Useful at the precise edge of dialling in.

Good to know

• The trade-off is slower coarse adjustment — going from espresso to filter takes many more turns.
• Worm gears are more mechanically complex; treat them gently and don't over-torque.