Windmills were used almost exclusively for pumping water, with enough water ideally stored to last at least three days, though they were also used in limited ways for grinding feed and running machines such as grindstones, lathes, and shellers when work could be done while the wind was blowing. Their tower posts were usually set in concrete at least five feet into the ground, wood towers were generally replaced by metal after 1890, and tower height ranged from 10 feet to 100 feet so the wheel would stand above nearby buildings, windbreaks, and hills within 500 feet. The wheel was a steel framework carrying wood or steel sails set at an angle of weather of twenty to thirty degrees, with wider sails of about twelve inches commonly used. Motion passed from the shaft to the pump rod either directly by a pitman-wheel connection in a direct connected mill or indirectly through spur gears in a back-geared mill. Because a pump should not run faster than forty strokes per minute, governors and automatic regulators controlled wheel speed and could turn the mill out of gear when a nearby tank was full, while a coiled spring helped hold the wheel at the proper angle in high or low wind. Windmills were mostly replaced by gasoline or electric pumps in the early 1900's, though they remained useful where power was unavailable and could also generate electric power. The Halladay design, common by the 1880's, used tilting blade sections to reduce speed, with blade banks lying flatter in light wind to capture more wind and slowly tilting forward as wind increased to keep speed constant; in an out of sail position, the wheel captured too little wind to spin. The tail kept the windmill facing the wind, and as it turned, a pitman-wheel connection pumped water into the barrel. Aermotor, which introduced an all-steel windmill in 1888 and had continuously manufactured windmills since then, made a back-geared mill and in 1916 introduced the Auto-oiled design, in which moving parts ran in a bath of oil and needed changing only once a year instead of weekly oiling.