The fantail is a device which automatically keeps the sweeps facing into the wind. Normally it is edge on to the wind but if the wind changes direction, the fantail turns and through a series of gears, the cap slowly turns to face the wind.

Before the fantail was fitted in 1840, the miller had to do it manually. After he had spread the canvas over the lattice framework of the sails, he hauled on a chain hanging down at the rear of the mill which turned the cap so that the sails faced the wind.