When should a jack be replaced instead of repaired?

The correct answer reflects the critical safety aspect of using jacks in various applications. When a jack exhibits significant structural damage, such as cracks, deformations, or compromised welds, it can lead to catastrophic failure during use. The integrity of the jack is paramount since it is responsible for supporting heavy loads. Any indication of structural compromise means that the jack may not perform reliably, which poses a serious risk to both the user and the surrounding environment.

In contrast, minor cosmetic damage does not typically affect the functional safety and lifting capacity of the jack, so it may not warrant replacement. Similarly, a jack's maximum lifting capacity refers to its design specifications rather than its condition. Lastly, having no visible damage signifies that the jack is in good working order, which doesn’t necessitate a replacement. Therefore, replacing a jack is essential primarily when structural integrity is at stake, ensuring safe operation.