The FasTen Leveling Block 10-pack allows you to stack the interlocking blocks to the desired height for safe and easy leveling. These blocks can be used with single wheels, double wheels, hydraulic jacks, tongue jacks, stabilizer jacks, 5th wheel jacks and tandem axles. They are also compatible with Camco's Leveling Blocks. They have a strong, durable construction and are engineered with a patent-pending design to optimize both strength and weight, resin is UV stabilized and built to last even when exposed to sunlight for extended periods of time.