Prussik diameter vs climbing line diameter


New Member
Karlstad Sweden
I'm a little confused as to what diameter is approved for safe use when tying a Prussik on the climbing line. Most lines from my suppliers seem to be between 11.7mm to 12.5mm (SRT lines only 11mm).

I understood the general rule to be that the Prussik should be half the diameter of the climbing line it is supposed to grab onto. But then the smallest approved Prussik was 7mm, and 9 was preferred, and then I don't understand what Prussik could be used at all


Well-Known Member
Lancaster, PA
Not half, slightly less. 1/8” or 2-3mm is fine. The smaller the hitch cord is compared to the host line the tighter it will sieze.

While there is no actual regulation for minimum diameter, 8mm for a hitch that will move when in use (climbing hitch) is generally accepted. As small as 6mm for stationary applications.

Where ever you heard the 1/2 stuff I would disregard and find a better source of information

Find a reputable hands on training course, a skilled mentor and some good books. Preferably all three. Youtube is a questionable training resource as for every good vid there are 10 shitty ones and without a point of reference...



Well-Known Member
Anything from 8 to 10mm will be safe as long as the hitch works reliably with your rope. However, usually, ~2mm smaller than your line will generally perform best, especially in terms of binding.

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