Prusik Hitches

Prusik Hitches

A Prusik hitch typically "fails" either by slipping along the main rope or breaking at varying kN (kilonewton) thresholds depending on whether you mean slipping (grip failure) or cord breakage (structural failure):

• Slipping Failure (When the Hitch Starts to Slide)

  • First Slip / Slipped Grip

    • A standard 6mm accessory cord Prusik tied on an 8-10mm rope will often begin to slip or creep under loads around 2 kN to 3 kN (depending on the number of coils, such as 3-on-2 vs 3-on-3 wraps)

    • Per Prusik, Auto Blocks, and Klemheist Break Tests by HowNOT2

    • 4MM PARACORD on 10.5mm Dynamic Rope:

      • Prusik broke at 3.74kN

      • Klemheist broke at 3.34kN

      • Auto Block 3 wraps slips at 1.34kN

      • Auto Block 4 wraps slips at 5.32kN

      • Paracord doubled twice broke at 8.90kN

      • Paracord in a loop broke at 4.06kN

    • 5MM ACCESSORY CORD on 10.5mm Dynamic Rope:

      • Prusik broke at 8.16kN 

      • Prusik broke at 5.36kN

      • Klemheist slips at 3.3kN  

      • Auto Block: 3 wraps slips at 0.36kN 

      • Auto Block: 4 wraps slips at 3.62kN 

    • 7MM ACCESSORY CORD on 10.5mm Dynamic Rope:

      • Prusik broke at 7.9kN 

      • Prusik slips at 5.18kN

      • Klemheist slips at 3.3kN and tangles up with rope at 11.62kN

      • Auto Block: 4 wraps slips at 0.8kN 

    • old HOLLOW BLOCK on 10.5mm Dynamic Rope:

      • Prusik broke at 5.84kN (note: old HollowBlock was used)

      • Auto Block: 3 wraps slips at 0.42kN 

      • Auto Block: 4 wraps slips at 1.38kN 

  • Higher Load Slips

    • In some rescue testing configurations (like a 4-on-2 PMI 6mm Prusik on an 8mm rope), initial slips occur around 7.0 to 7.3 kN, eventually peaking near 9 to 10 kN before the cord fails inside the hitch

  • Self-Limiting Behavior

    • In climbing scenarios (like a cow-tail sling), a Prusik will intentionally slip under high impact loads, which helps absorb energy and cap the force transmitted to the climber well below dangerous thresholds

• Breaking / Structural Failure (When the Cord Snaps or Glazes)

  • Accessory Cord Tensile Strength

    • Standard 6mm to 7mm accessory cords typically have a free-length Minimum Breaking Strength (MBS) in the 7 kN to 10 kN range

    • Tied into a loop and loaded over a small radius, the knot configuration reduces the overall system strength

  • Melt-Through / Glazing

    • If a Prusik slides too far or too fast under a heavy load, the extreme friction generates intense heat, causing the sheath of the accessory cord to glaze, melt, or burn through long before reaching its static breaking point

    • HMPE/Dyneema is MORE susceptible to melting

    • Aramid is LESS susceptible to melting

  • Full Breakage

    • Studies on traditional Prusiks (such as 7mm cord on 11mm static line) show average breaking strengths around 12.36 kN

    • Heavy-duty configurations can range higher depending on cord material and diameter

Nylon Accessory Cord

• Prusik cord should generally be about 60% to 80% than the diameter of the main rope

  • Roughly 2mm to 3mm smaller than main rope

  • Minimum 5.5-6mm

  • Max 7mm

• Soft and Supple

  • Squeeze a bite of cord and the eye should just about disappear

• Regular cord from big retail stores won't work

  • Go to REI or climbing shop

• Breaking Strength

  • 5mm: 5.5 kN 

  • 6mm: 7.5 kN 

  • 7mm: 13 kN 

• Slippage Threshold

  • Generally slips rather than breaks under high or excessive loads

    • Heavily influenced by main knot used, rope's diameter, sheath treatment and whether rope is wet, dry, icy or slippery

  • 4mm or 5mm accessory cord or fewer wraps of larger cord will slip at lower forces 

    • Starting around 1.3 kN to 3.0 kN

  • 7.5mm on 11mm Rope slips at higher forces

    • 3-wrap Prusik often experiences its initial point of major slippage around 5.5 kN to 8.7 kN

• Selecting a Size

  • 5 mm

    • Can provide aggressive gripping

    • Has less material and generally less breaking-strength margin

    • Often NOT recommended

  • 6 mm

    • A good balance of grip, strength, and handling

    • Commonly recommended for Prusiks on modern climbing ropes

  • 7 mm

    • Offers greater cord strength in many constructions

    • Strong enough to be used as an anchor or other rescue uses

    • May require additional wraps or a different host-rope combination to grip reliably

• Lengths needed

  • 5mm to 6mm nylon or aramid cord joined with a double fisherman's bend

    • Abseil / Rappel Backup (Third Hand)

      • 30-35cm Loop (~1.2 meters / 4 feet of cord) 

    • Ascending or General Progress Capture 

      • 40-50cm Loop (~1.5 meters / 5 feet of cord) 

    • Foot Loops or Special Rigging 

      • 1-2 meters / 3-6 feet of cord

  • 7mm nylon for anchor and rescue use

    • Quad Anchor

      • 14 feet of 7mm cord makes a loop close to 190cm

      • ~17 feet of 7mm cord is needed for a 240m loop

    • Masterpoint

      • 21 feet of 7mm cord makes around a 300cm loop

    • Self Rescue

      • 20+ feet of 6-7mm cord

• Examples:

  • Mammut Pro Cord (6 mm)

    • Diameter & Material: 6 mm kernmantle construction, 100% nylon.

    • Strength: 7.5 kN (1,686 lbs) minimum breaking strength.

    • Weight: 22 g/m.

  • Sterling 6 mm Nylon Accessory Cord

    • Diameter & Material: 6 mm kernmantle construction with a 100% nylon core and sheath.

    • Strength: 8.2 kN (1,843 lbs) minimum breaking strength (MBS), according to Sterling's published specifications.

    • Weight: Approximately 23 g/m.

  • Mammut 7 mm Accessory Cord (7.0 Cord)

    • Diameter & Material: 7 mm, 100% polyamide (nylon) kernmantle construction

    • Strength: 13.5 kN (3,035 lbs) minimum breaking strength

    • Weight: 30 g/m

  • Sterling 7 mm Nylon Accessory Cord

    • Diameter & Material: 7 mm kernmantle construction, 100% nylon

    • Strength: Approximately 12.4 kN (2,787 lbs) minimum breaking strength

• NOT Appropriate for Prusik Hitches:

  • BlueWater 5.5 mm Titan Cord

    • HMPE/Dyneema and nylon construction

    • NOT ideal for Prusik Hitch

    • Low Melting/Heat Resistance Issues: Dyneema/HMPE has a low melting point. If used in a traditional binding Prusik where heavy friction builds up (such as rappelling with a Prusik backup under high speed or load), the cord can glaze, melt, or fail to grip properly compared to aramid/Kevlar-blend cord (like a Bluewater VT Prusik or Sterling Hollow Block).

    • Stiffness and Knot-Holding: Titan cord is quite stiff and slick compared to soft nylon or aramid/tech cords. Traditional knots like a classic three- or four-wrap Prusik can be difficult to set, tend to slip or fail to bite reliably on standard single ropes, or conversely lock up too rigidly depending on the host rope diameter.

  • Sterling 5.9 mm PowerCord

    • Diameter & Material: 5.9 mm with a braided Technora core and nylon sheath

      • Technora Heat Resistance: Withstands continuous temperatures up to 200°C (392°F) and has a thermal degradation threshold above 500°C (932°F)

    • NOT ideal for Prusik Hitch

    • Stiffness and Memory: It features a high-tenacity Technora core and a nylon sheath, making it very stiff and static with a noticeable "memory," which prevents it from being supple enough to easily bite and grip a main rope

    • Slickness: The lack of flexibility and the smooth high-strength core/sheath interaction mean it struggles to set and release smoothly as a friction hitch

Sewn Prusik Cord 

• 7mm max size for most climbing

• 8mm used with 11mm static ropes which are in turn used for rescue

• HollowBlock2 (Sterling Rope):

  • 6.8mm square shaped hollow braid

    • Aramid fiber

    • For use on 7 mm or larger rope

  • Breaking Strength: 14kN 

  • Sizes

    • 13.5-inch (34 cm) loop 

      • Traditional prusik knot 

      • Standard wrap-around-the-leg autoblock (rappelling backup / third hand)

    • 19-inch (48 cm) loop 

      • French Prusik

      • Klemheist knot

      • More complex multi-wrap friction hitches for rescue use

• BlueWater VT Prusik

  • Structured cord with an aramid sheath

  • Kernmantle-style construction with an aramid sheath over a core (often sewn eyes/loops)

    • Longer working life compared to the sheathless HollowBlock

  • Breaking Strength:

    • BlueWater 8mm VT Prusik Basket (looped / both eyes clipped) 29.5 kN  

    • BlueWater 7mm VT Prusik Basket (looped / both eyes clipped) 22.6 kN

  • Tied as a Valdotain Tresse (VT) or asymmetric/wrap-and-braid style hitch

    • Takes slightly longer to dial in and tie properly than an French Prusik (autoblock)

  • Smoother release and better hand feel during operation than HollowBlock

• Beal Jammy

  • 5.5mm diameter

    • Polyamide (nylon) sheath

    • Aramid core

  • Breaking Strength: 22 kN

  • 35cm length - traditional Prussic

  • 50 and 60cm - French Prusik or Klemheist

  • It is important that your knot is well dressed, or your Prusik will slide and bunch up