As Lester posted, the 22.2 mm is the diameter of the quill and that the correct size to fit inside a 1" steerer tube. The 24.5 or 26 mm is the diameter of the handle bar clamp and you buy the one that fits your bars. The 85 mm reach is the distance from the center of the quill's bolt head to the center of the handlebar clamp measured along the stem. That's a relatively short stem so be sure it won't put the bars uncomfortably close when you angle the stem up.