Possible Clues:

• Bevel gear used on cars' rear axles
• Sort of gearing for gap in rates
• Not the same in The Gulf
• Gear train which allows wheels on the same axle to rotate independently
• Sort of gear — sort of equation
• Learned if fit for changing this sort of gear
• Distinguishing gear
• Gear that's demanded by skilled workers?
• Gear found on the rear axle of cars
• Kind of equation in which odd imaginary number is written above a line