Leveling Scissor Jack has a heavy-duty steel construction. Each jack includes a large 5 inch by 8 inch rectangular steel base plate and frame mounting plate that is supported by its own channel. All scissor arms engage with a tooth gear design to ensure straight line vertical extension and retraction. One model will fit most RVs regardless of the ground-to-frame clearance with 4 inch to 23-3/4 inch extension. 7,500 pounds capacity.