Stems: angles and lengths and whatnot

[aj1152]

So yesterday I was thoroughly confused about stems. I saw 110 mm, 120 mm, and 130 mm, but what is that measuring exactly? Is it from center of the fork to the center of the handlebar, from the very front of the stem to the very end of it, or is it something else?

Also, what's with all the angles? I saw 17 degrees, 10 degrees, 80 degrees, and on and on. What's that based on?

[Wrench Goode]

The length is measured from center to center, center of the handlebar to the center of the steer tube (where the stem would slide onto the fork). Angles are degrees of rise from zero. Zero being parallel to the ground or level. To get more in depth some companies use 90 degrees as zero. For example an 86 degree stem is the same as a 4 degree stem. Two ways to say the same thing.