Most keyboard trays require a 21" or 22" track to be able to be stored completely under the desk when not in use.   Many of our brands, including Humanscale, ESI Ergonomics and Workrite offer shorter tracks but if you use a standard mechanism with a shorter track your keyboard tray will still protrude when pushed all the way in.  The keyboard tray systems in this section all feature a short mechanism, and are designed for shallower installations and stow completely on a 17" or 17 3/4" track.