Part 393: Parts & Accessories

Learn about the parts and accessories necessary for safe operation of commercial motor vehicles.

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Part 393: Parts and Accessories Necessary for Safe Operation

Part 393 details the minimum requirements for parts and accessories necessary for safe operation of commercial motor vehicles. This includes requirements for lighting devices, brakes, tires, wheels, coupling devices, and more. Understanding these requirements is essential for performing accurate DOT annual inspections.

What You'll Learn

Lighting Devices

  • Headlamps - requirements, mounting, aiming
  • Tail lamps - visibility requirements
  • Stop lamps - brake light specifications
  • Turn signals - flash rate and visibility
  • Clearance lights - identification lamps
  • Reflective devices - marking requirements

Brakes

  • Service brake systems - hydraulic and air
  • Parking brake requirements
  • Brake hoses and tubing - inspection criteria
  • Brake adjustment standards
  • ABS requirements

Tires and Wheels

  • Tire tread depth requirements
  • Tire condition standards
  • Wheel and rim requirements
  • Tire inflation standards
  • Matching requirements

Coupling Devices

  • Fifth wheel requirements
  • Pintle hooks and hitches
  • Safety chain requirements
  • Drawbar and trailer connections

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