Abstract: A precision grass mower of the triplex reel type operating from a common tractor-type power source, each mower unit having an adjustable ground engaging roller for cutting golf greens at a precisely predetermined height. Each of the reels of the mower is provided with manually actuated, automatically operated shifting means for moving the height adjusting roller to either of two positions for cutting the grass of the green and of the collar surrounding the green at different but precisely determined heights. The shifting means of all of the mower reels are instantly and simultaneously actuated and operated by fluid pressure.