Parts of a Windmill Diagram – Sails, Cap, Fantail and Gears

All 15 parts on the diagram

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Start here: 7 main parts 7

Sails The frames that catch the wind and turn the windshaft.
Cap The top of the mill, which turns the sails into the wind.
Tower The fixed body of the mill, built of brick or stone.
Fantail A small wheel behind the cap that turns it into the wind.
Windshaft The axle turned by the sails; it carries the brake wheel.
Brake wheel The big gear on the windshaft; a brake grips its rim.
Runner stone The upper millstone, which turns.

The mill from outside 2

Stage A platform round the tower, from which the miller tends the sails.
Stocks The long timbers, fixed through the windshaft, that carry the sails.

The mill cut through 6

Wallower The gear atop the upright shaft, driven by the brake wheel.
Upright shaft The tall shaft down the middle, carrying the drive to the stones.
Great spur wheel The wide gear on the upright shaft that drives the stone nuts.
Stone nut A small gear that drives one pair of stones.
Bedstone The lower millstone, which stays still.
Hopper A funnel above the stones that feeds the grain to them.

How this list was compiled: Read 2026-09-30; a name is kept only where two of these use it. (1) Wikipedia, Windmill (the horizontal windshaft carries the sails; the brake wheel is fitted on the windshaft and has the brake round its rim; it drives the wallower at the top of the vertical upright shaft; the great spur wheel, lower on the upright shaft, turns one stone nut or more on the shaft of each millstone; the cap), Tower mill (a brick or stone tower with a cap that rotates to bring the sails into the wind; stock; gallery), Windmill fantail (a small rear windmill at right angles to the sails, which turns the cap automatically) and Windmill sail. (2) R. J. Brown, Windmills of England (1976), https://archive.org/details/windmillsofengla0000brow , read as passages through the Internet Archive's full-text search: fantail, windshaft, brake wheel (the largest gear), wallower, upright shaft, great spur wheel, stone nuts, stocks (two heavier timbers set at right angles through the windshaft), whips, the curb the cap turns on, the stage from which the miller adjusts the sails, hopper; millstones were in pairs, only the upper runner stone revolved and the lower bed stone was stationary. (3) John Vince, Discovering Windmills, https://archive.org/details/discoveringwindm0000vinc , read the same way: its gear diagrams list windshaft, brake wheel, wallower, vertical shaft, great spur wheel, stone nut, hopper, runnerstone and bedstone; fantail, cap, curb, stage and gallery in its text. (4) F. H. Shelton, Windmills, Picturesque and Historic (1919), https://archive.org/details/windmillspicture00shel : sails or sweeps, the great shaft and great wheel, the pinion or lantern or trundle or wallower wheel on a vertical shaft, mill stones, the cap, tower mills. (5) Peter Barlow's description quoted in Brangwyn and Preston, Windmills (1923), https://archive.org/details/windmills_202003 (wind shaft, whips, brake-wheel and its brake), and Knight's American Mechanical Dictionary (1882), https://archive.org/details/knightsamericanm03knig (sails, whips, the windmill-cap, upright shaft). Licence: own work

The drawing: Drawn for this site on 2026-09-30 from plain geometry; nothing traced. A schematic, not to scale. Licence: own work

How it works

This parts of a windmill diagram shows the old kind of mill, built to grind grain into flour. The names are the ones English millers used. A modern wind turbine, which makes electricity, has a page of its own.

Read the full guide

Outside the mill

The sails catch the wind. They are fixed to long timbers called stocks. The cap is the top of the mill, and it turns on the tower so that the sails face the wind. The fantail, a small wheel behind the cap, does the turning. The stage is a platform the miller stands on to reach the sails.

Inside: from the wind to the stones

The sails turn the windshaft, and the brake wheel turns with it. Its cogs drive the wallower, which turns the upright shaft down the middle of the mill. Lower down, the great spur wheel drives a stone nut for each pair of millstones. Grain runs from the hopper between the turning runner stone and the fixed bedstone.

Only the top stone turns. The runner stone runs; the bedstone stays in bed.

Questions and answers

What are the parts of a windmill called?

Outside: the sails, the cap that carries them, the tower, and often a fantail and a stage. Inside: the windshaft, the brake wheel, the wallower, the upright shaft, the great spur wheel, the stone nuts and the millstones, with a hopper to feed them.

What are the blades of a windmill called?

On an old windmill they are called sails. The first ones were wooden frames with cloth spread over them, like a ship's sail. Later kinds have rows of small shutters instead of cloth.

What is the top of a windmill called?

The cap. On a tower mill the brick tower stays still and only the cap turns, carrying the sails and the windshaft round with it so that the sails always face the wind.

What does the fantail on a windmill do?

It turns the cap by itself. The fantail is a small wind wheel set at right angles to the sails. When the wind shifts, it starts to spin, and its gears wind the cap round until the sails face the wind again.

What is the difference between a windmill and a wind turbine?

A windmill uses the wind to do a job on the spot, such as grinding grain or pumping water. A wind turbine uses it to turn a generator and make electricity.