What characterizes a prusik knot?

A prusik knot is specifically characterized by its construction using a rope of a smaller diameter than the rope it is attached to. This is essential because the smaller diameter allows the knot to grip the larger rope securely. The design of the prusik knot relies on the friction created between the two ropes, facilitating a mechanism where the prusik can slide when under minimal load but will lock firmly in place when a load is applied.

Using a rope of the same diameter would not provide the necessary friction and gripping action required for the knot to function effectively. Conversely, using a larger diameter rope would decrease the likelihood of the knot holding when a load is applied, rendering it unsafe for use in rescue operations. Additionally, the mention of a metal-based device is not relevant to the intrinsic properties of the prusik knot itself, as it is a knot made from climbing rope, emphasizing the importance of rope selection based on diameter for the knot's effectiveness in rescue situations.