What diameter prusik cord is recommended as an ascending device on a 12.5 fixed line?

The recommendation for an 8 mm or 9 mm prusik cord as an ascending device on a 12.5 mm fixed line is based on the optimal balance of grip and ease of use. Prusik knots rely on the friction generated between the prusik cord and the fixed line to hold securely during ascent or descent.

Using a diameter that is generally about two-thirds the size of the main line, like 8 mm or 9 mm for a 12.5 mm line, ensures that the prusik knot will grip effectively without being too loose or overly tight. This size range strikes a practical balance, offering reliable performance in a variety of rescue scenarios while also allowing for easier manipulation when ascending.

Choosing a cord that is too small can lead to insufficient grip, whereas a cord that is too large could make the prusik knot difficult to release or may not grip effectively at all. Additionally, the 8 mm and 9 mm sizes provide enough strength for the demands of rescue operations while still being lightweight and manageable for field use.