Originally Posted by big john

Quill stems are the older, archaic type. Modern bikes use threadless headsets and clamp on stems because they are lighter, stronger, and better in just about every way.
With the threadless setup, the bar height is determined mostly by the length of the steertube,the part of the fork that the stem clamps on to. If you have an ideal frame, except the bars are too low, get a new fork and don't cut the steer tube until you find your position.