What size prusik cord is recommended for a 12.5mm rescue line in belay operations?

For belay operations using a 12.5 mm rescue line, an 8 or 9 mm accessory cord is commonly recommended for prusik knots. This sizing is crucial because the prusik needs to grip effectively on the main line, and the friction created by the prusik knot is influenced by the diameter of the cord used.

An 8 or 9 mm accessory cord is typically small enough to create sufficient friction when wrapped around the 12.5 mm rescue line, ensuring that the prusik can hold securely under load while still being manageable for retrieval. This size also balances the need for strength and weight, which is vital in rescue scenarios where gear must be light and strong.

Using a prusik cord that is too thick, such as a 10 mm or larger option, would decrease the effectiveness of the knot to grip the main line securely, possibly leading to slippage. Conversely, a cord that is too thin may not provide adequate strength and could break under load. Therefore, the recommended size ensures both efficiency and safety in the application.