Related Clues:

• Effective power
• They work when engaged
• They're engaged!
• Wheel projections
• Industrial revolution elements?
• First, second and third
• Some canines
• Choppers, so to speak
• Sprocket projections
• First and second, for two
• Canines, e.g.
• Machinist's teeth
• Transmission innards
• Saw things?
• Working parts of a saw