Related Clues:

• A semi lacks a front one
• Shaft under the floorboard
• Bobbin, e.g.
• Spinning reel part
• Drivetrain component
• Bar between Pirellis
• Linchpin's setting
• One of two on a car
• Chassis rod
• Drivetrain element
• Part of a wheelset
• Thread
• A unicycle has one
• Car shaft
• Bar in a car