Glossary of terms

Glossary of terms

Don't know your spur wheel from your stone nut? Here’s what some of the main windmill words mean.

The bottom millstone, which doesn’t move.  The runner stone spins on top of it, grinding the grain into flour.

Brixton Windmill mill stone

A container that holds the grain, on the bin floor (third floor) of the mill

As the name suggests, this stops the sails from turning. To operate the brake you would pull a level connected to the rim of the brake wheel.

The brake

This is near the top of the mill, the first wheel in the series of gears that powers the mill and is attached to the windshaft so it’s turned directly by the sails. It drives the wallower (the big wheel that drives the vertical shaft), gripping the outside of it to slow the mill. The brake wheel is usually made of wood.

The brake wheel

Joins the main timbers of the sails to the windshaft. It’s an iron device made of two open-ended boxes at right angles to each other. Also called a poll end.

poll end - from a windmill

Right at the very top of the windmill, it’s made of wood looks like an upside-down boat.  It turns so the sails can point into the wind and it contains the brake.

The Cap of the windmill

Metal wheels that keep the cap centrally within the curb.

The curb

The earliest and most powerful type of sail. It has a sheet of cloth stretched over a wooden frame, a bit like you would have a sail on a ship. See more about the different kinds of sails.

The common sail

A metal rim that supports the cap on top of the tower. It is fitted with rollers so that the cap can turn more easily.

The curb

The central hole in the runner stone where the grain is poured in.

The windmill eye

The best type of stone for grinding grain, used throughout Europe. Fairly expensive small pieces of stone are set into plaster of Paris.

The Burr

A set of spinning balls that use centrifugal force to push levers that keep the gap between the grinding stones constant as the wind changes speed.


The name for any grain that is fed into the stones. This is where the expression “it’s all grist to the mill” comes from.

A large, usually wooden funnel that stores the grain and then feeds it down into the stones.


The name for any grain that has been ground by the stones.

A type of stone used for the grinding stones in windmills.  Also known as peak, grey or gritstone, usually from the Derbyshire Peak District.

The Brixton Windmill millstone in summer

Sails with shutters with a spring so each sail can be adjusted individually, without stopping the mill (unlike common sails). Most popular design patented by William Cubitt of Norfolk in 1807. See more about the different kinds of sails.

patent sail

The earliest type of European mill, which was mounted on a post. The whole mill turned around the post to face the wind. These were not as strong as smock mills like Brixton Windmill where only the top of the building turns.

A freestanding cast-iron mill first driven by steam and then by gas.

Provender Mill

The shaft that turns the runner stone. Usually square to shake the grain in.


The top millstone, which turns on top of the bed stone, grinding the grain.

The runner stone

Wind-powered mechanism for lifting sacks of grain to the top of the mill.

Sack hoist

The ‘arms’ of the windmill that are turned by the wind. They could be common sails or patent/spring sails.

Brixton Windmill sails after restoration

This feeds grain from the hopper into the eye of the runner stone.

Windmill shoe

A kind of wooden mill, usually hexagon or octagon-shaped, with a cap that rotates to turn the sails into the wind.

Smock mill

Opening the sail shutters to let wind flow through them, usually because there are gusts of wind that are too strong.

A large cog near the bottom of the upright shaft, which drives the stone nuts or other machinery gears. Also the name for any cog with teeth sticking out rather than up.

Spur from the windmill

There are two millstones in a windmill, the runner stone on top of the bed stone, that grind the grain to make flour.

The cutting of grooves on the grinding surface of the millstone. The grain is ground as it catches on these grooves while the stones are spinning.

Dressed stones from a windmill

A small cog at the top of the quant that transfers energy from the spur wheel to the stones.

stone nut from a windmill

This expression means the sails are facing the wrong way, and they could be blown off!

A set of long levers which, with a turn of a screw, can lift or drop the heavy runner stone to be closer or further away from the bed stone, affecting how fine the flour will be when it comes out.

governor and tentering gear

A tower of brick or stone containing mill machinery.  It stays still and only the cap at the top and the sails turn to face the wind.

Brixton Windmill

A term meaning that the stones are driven by gears on the floor below.

The main shaft down the centre of the tower, taking power from the wallower at the top to the spur wheel near the stones.

The wooden casing enclosing the millstones.

windmil vat

The first gear in the vertical shaft of the mill. The brake wheel turns the wallower and transfers energy from the horizontal windshaft to the vertical upright shaft to drive the millstones.


The horizontal axle at the top of the mill, the sails and the brake wheel are fastened onto it by either a cross or a canister. The rod to control patent sails runs through the hollow centre.