Which jack is the least stable and prone to failure under heavy loads?

• A. Scissor jacks
• B. Bottle jacks
• C. Hydraulic jacks
• D. Ratchet lever jacks

Answer: (D)

Stability under heavy loads depends on base area and how the load’s weight is distributed. A small base and a tall, narrow lifting member create a high center of gravity and a larger tipping moment, making the jack more prone to movement or collapse when stressed.

The ratchet lever jack fits this less-stable pattern: it uses a compact base and a tall, slender column with a lever-driven mechanism. With a heavy load, the weight sits high and the footprint is limited, so even slight surface irregularities or lateral shifts can cause tipping or load drift. The ratchet action itself doesn’t provide the same locking stability under heavy, dynamic loads as a hydraulic system, so a misalignment or partial release can lead to a sudden drop or failure.

In contrast, bottle jacks and hydraulic jacks are designed for heavier lifts with a lower center of gravity and larger contact bases, which improves stability. Scissor jacks distribute load through their expanding legs, which can be more stable than a tall, narrow lever jack, though stability can still degrade at height.