This is the Rotating Back Pad for the BC Strength Thruster 3.0. 

Rotating Back Pad Specifications

• Approx dimensions: 12" wide x 28” long x 5.5" high
• Approximate weight: 30 lbs
  
• Color: Fine-textured black powder coating
• Padding color: Black
• Heavy-duty steel construction with nickel/chrome plating
• Heavy-duty commercial grade foam padding and upholstery