Briscoelab wrote:4. Some companies are notorious for well documented stem length variances. 3T ARX for example, are ~8mm long on their -17 stems. This was likely a mistake in the forging design when someone wanted to account for the angle.
3T have their own way of measuring stems - instead of measuring the actual stem length, they measure the extension from the steerer axis (the shortest distance from center of handlebar to steerer axis, so it's measured at 90 degrees to the steerer regardless of the actual stem angle). This means that the further the stem is from 0 degrees, the bigger the difference will be between the actual and nominal lengths.