Rail clamping wheel block. A Super Chock for railcars, and overhead cranes. High-security wheel blocking. Clamps grip rail head through wedge action. Use one chock at each end of the car. For added security, padlock can be field-installed. Fits all wheel sizes. For rails 60-100 pounds. Do Not Use for impact-stopping. Weight: 45 pounds. Product of Aldon ® Company.