These chocks are the solid bottom version of RC450. Both are general purpose chocks that are the utility industry standard. The chocks are composed of durable rubber so they are stronger and safer in industrial applications. They are also resistant to UV damage, weather and damage from moisture, salt, and oils. Their excellent traction gives helps provide a sure grip between the tire and road to reduce tire and pavement damage. They are designed so that either side can be positioned against tire. Most often used in construction, utility, and other commercial industries.