Related Clues:

• They're shifted
• Teeth on a wheel
• Transmission units
• Swiss watch parts
• Teeth that aren't flossed
• Meshing parts
• Car-transmission settings
• Lowly workers, figuratively
• Bit players
• First, second, etc.
• Bicycle parts
• They often get engaged
• Tenspeed features
• Parts of the machine, maybe
• Four-on-the-floor options