Blueprint-style diagram of a wire rope sling assembly with a close-up detail of the thimble and shackle on a dark grid

Glossary

Rigging and lifting terminology used across our product pages — the definitions applied in DIN, EN and US practice.

Loads and ratings Components and materials Inspection and traceability Installation and rigging practice

Loads and ratings

Working Load Limit WLL

The maximum load a component may carry in service, as set by the manufacturer or the applicable standard. It is the figure that appears on the marking and in the catalogue, and it must never be exceeded.

Safe Working Load SWL

An older term for the same concept as WLL. It has largely been replaced by WLL in modern standards and manufacturer documentation; both refer to the load permitted in service, not to the load at which the item breaks.

Minimum Breaking Load MBL

The lowest load at which a component is expected to break when tested to destruction on a sample basis. It is a test criterion, not a working figure — equipment is rated by WLL, not by MBL.

Design factor / Safety factor

The ratio between the minimum breaking load and the working load limit. A component with an MBL of 60 kN and a WLL of 10 kN has a design factor of 6. The required factor is set by the application, the standard and the national regulation — not by the seller alone.

Proof load / Proof test

A load applied to a component during manufacture or periodic examination to verify it can sustain the load without permanent deformation. It is normally a multiple of the WLL and is held for a defined time. Proof testing is not destructive and does not replace the design factor.

Shock loading

A load applied suddenly, or a load that changes rapidly in magnitude, producing forces well above the static weight being lifted. Snatching, sudden braking and swinging all create shock loads. Equipment rated for a static load can fail under a much smaller shock load.

Side loading

Loading a component at an angle to its intended axis. Many rigging components — hooks, shackles and eye bolts in particular — lose a substantial part of their rated capacity when loaded off-axis, because the load is no longer carried by the section the rating was based on.

Termination efficiency

The strength of a rope termination expressed as a percentage of the rope's minimum breaking load. A spliced or swaged termination retains a high proportion of the rope strength, while a U-bolt clip termination retains considerably less — which is why clip terminations are restricted in standards.

Wire rope thimble DIN 6899

A grooved metal insert placed inside a rope eye to hold the eye's shape and protect the rope from wear at the point where it bears on a shackle, hook or pin. Without a thimble, the rope bears directly on the fitting and the eye wears and deforms.

Preload

The tension deliberately introduced into a fastener when it is tightened. In a clip termination, correct preload — achieved by torquing to the specified value — is what generates the friction that holds the rope.

Duty cycle

How often and how heavily a piece of equipment is used, usually counted in load cycles. Re-inspection and re-tightening intervals for rope terminations are set by duty cycle rather than by calendar alone.

Minimum Breaking Strength MBS

The lowest load at which the item fails in a standard tensile test. It is a laboratory result and is always a multiple of the WLL — design to the WLL, never to this figure. Often written MBL when the item is a rope or chain rather than a discrete component.

Grade 80 / Grade 100

The strength classes used for alloy steel chain. Grade 80 is rated at 80% of the minimum breaking stress of the chain size, Grade 100 at 100%. The number is a strength class, not a grade of steel in any other sense, and it appears on the chain's identification.

Sling angle

The angle between the sling leg and the horizontal. This is the reference used by ASME B30.9, and it is the opposite convention to an angle quoted from the vertical. The same lift is 30° or 60° depending on which way it is measured, and the capacity differs by a factor of two between those readings.

Included angle

The angle measured between the two legs of a sling, which is 90° minus twice the sling angle only when the legs are equal. It is frequently quoted in rigging manuals alongside the sling angle, and reading one as the other is a common cause of miscalculated capacity.

Choker hitch capacity factor

A choker hitch derives most of its capacity from friction at the point where the sling tightens on the load, and the bending stress at that point is why its rating is commonly taken at 75% of the sling's vertical rating. Reducing it further for angle compounds the two effects.

Coplanarity

Whether all the attachment points of a multi-leg sling lie in one plane. Four-leg slings rarely share load equally, so unless coplanarity has been confirmed the conservative assumption is that only two legs are carrying.

Proof force

The force, expressed in kilonewtons, applied during proof testing. It is a manufacturing test figure and is a different number from both the working load limit and the minimum breaking force, though certificate documents often list all three together.

Throat opening

The internal gap of a hook or a shackle bow. It increases permanently when the item has been overloaded, so it is measured against the manufacturer's original dimension rather than judged by eye.

Safe Working Load vs Working Load Limit

Two names for the same quantity. SWL is the older usage and still appears on drawings, lifting plans and certificates issued before the change to WLL; WLL is what current standards and most manufacturer documentation use. Neither refers to the breaking load.

Components and materials

Dee shackle vs bow shackle

A dee shackle has a narrow, D-shaped body and takes load mainly in line with the pin. A bow (anchor) shackle has a wider, rounded body that accepts load from several directions and can take slings side by side, but its rated capacity is reduced when the load is applied away from the centre line.

Screw pin vs bolt-type shackle

A screw pin shackle has a pin that threads directly into the body; it is quick to fit and remove, and is intended for applications where the pin is not subjected to rotation or drag. A bolt-type shackle uses a nut and a cotter (split) pin, which prevents the pin from backing out under vibration, rotation or dragging.

Turnbuckle, open body DIN 1480

The DIN pattern with an open, skeletal frame so the thread engagement of both end fittings is visible. Because the engagement can be seen, the open body is the pattern most often specified where the fitting has to be inspected while in service.

Turnbuckle, closed body DIN 1478

The DIN pattern with a closed, tubular body. It is stiffer and protects the thread from dirt and damage, but the thread engagement of the end fittings cannot be seen from outside.

Wire rope clip: saddle and U-bolt

A wire rope clip has three parts — a U-bolt, a saddle (the forged seat) and two nuts. The saddle must sit on the load-bearing (live) part of the rope and the U-bolt on the dead end. Fitting it the other way round damages the live rope; the traditional reminder is: never saddle a dead horse.

U-bolt wire rope grips EN 13411-5

The European standard covering U-bolt rope grips (terminations) for wire rope slings. Its scope is limited: grips to this standard are intended for static loads and for a single lift only, not for repeated re-use as a termination. Slings intended for repeated lifting use a swaged or spliced termination instead.

Wire rope clip, malleable DIN 741

The German standard pattern for a light malleable-iron wire rope clip. It is widely used for light-duty and general-purpose fixing — guarding, fencing, guy lines and similar — and is not intended as a lifting termination. Clips used to form a lifting eye must be to a standard that covers that use.

Eye bolt (collared / shoulder type) DIN 580

The German standard for a lifting eye bolt with a collar (shoulder) that must seat flat on the load. The collared type tolerates a limited amount of angular pull; a plain, uncollared eye nut pattern does not. Eye bolts are rated for axial load — angular loading reduces capacity sharply.

Eye nut DIN 582

The German standard pattern for a lifting eye nut — a female-threaded lifting point that screws onto a stud or bolt rather than into a tapped hole. As with eye bolts, the rating applies to axial load only.

Snap hook DIN 5299

The German standard covering snap hooks, with form C and form D being the patterns most often traded. A snap hook has a spring-loaded gate and is not a self-locking connector: it is not a substitute for a self-locking hook or a screw-gate connector where an unintentional opening could release the load.

Forged vs cast

Forged components are shaped from solid steel under pressure, producing a grain structure that follows the part's shape; castings are poured into a mould. For load-bearing rigging hardware, forging is the normal route because it gives more consistent strength and reveals fewer internal defects.

Hot-dip galvanising vs electro-galvanising

Hot-dip galvanising immerses the finished part in molten zinc, giving a comparatively thick, metallurgically bonded coating suited to outdoor and marine exposure. Electro-galvanising deposits a much thinner layer electrolytically, giving a brighter finish but less corrosion life.

Corrosion and section loss

Corrosion removes metal from the load-bearing section, so a corroded component carries less load than its marking states. Surface rust that can be wiped away is different from pitting and section loss: pitted, thinned or cracked hardware is taken out of service rather than re-rated.

Galvanic corrosion

Accelerated corrosion that occurs when two dissimilar metals are in electrical contact in the presence of an electrolyte such as seawater. It is why stainless hardware is not mixed indiscriminately with galvanised hardware, and why storage keeps metals apart.

Hydrogen embrittlement

Loss of ductility in high-strength steel caused by hydrogen absorbed during acid pickling or electroplating. It is a reason why high-strength components use a non-electrolytic coating, or are baked after plating.

Quenched and tempered

A two-stage heat treatment: the steel is quenched to harden it, then tempered to restore toughness. It is how alloy rigging steel reaches a higher strength than plain carbon steel.

Austenitic stainless, general grade AISI 304 / A2

The general-purpose austenitic stainless used for rigging in normal atmospheric and indoor environments. It resists corrosion well in clean air but is susceptible to pitting in chloride exposure.

Austenitic stainless, marine grade AISI 316 / A4

The molybdenum-bearing austenitic grade used for marine and chloride exposure. It resists pitting significantly better than 304 and is the usual choice for yacht rigging and coastal installations.

Rope lay and direction

The way the wires and strands are laid up in a rope, and the direction of that lay. It matters when fitting terminations and when matching replacement rope to existing rope: mixing lay directions can cause the rope to unlay under load.

Inspection and traceability

Batch / heat number

The identifier that ties a finished batch back to the melt, the material certificate and the inspection records. Traceability is only meaningful if the number on the certificate can be reconciled with the marking or record on the delivered goods.

Inspection document types EN 10204

The European standard defining the types of inspection document supplied with metallic products. Type 2.1 is a declaration of compliance with no test results; 2.2 gives results from non-specific (routine) inspection; 3.1 gives results from the specific batch supplied, validated by the manufacturer's independent inspection representative; 3.2 adds validation by the purchaser's representative or a designated third-party inspector.

Certificate of conformity

A document in which the manufacturer states that the delivered goods conform to the order and to the named standard. It is a statement of compliance, not a set of measured results — if you need measured chemistry or mechanical properties, specify the inspection document type (see EN 10204) at the time of order.

Marking and traceability code

The permanent marking stamped or forged onto the component — normally the size, the WLL, the manufacturer's identification and a traceability code. Standard-pattern hardware is expected to carry the marking required by its standard so the item can be identified and traced after it leaves the factory.

Quarantine and withdrawal criteria

The defects that require a component to be withdrawn from service immediately: cracks, distortion, a worn or opened-out throat or eye, a seized or damaged thread, a missing or illegible marking, heat damage, and corrosion with pitting. A component with no legible marking cannot be identified, and is withdrawn.

Torque wrench

A tool that tightens a fastener to a set turning force rather than by feel. Clip terminations should be tightened with one: under-torqued nuts let the rope slip, over-torqued nuts damage the thread or the body.

Competent person

The term used in lifting regulations for someone with the training, knowledge and practical experience to carry out a specific task — such as examining equipment or setting an inspection interval — and to recognise when it is unsafe to continue.

Installation and rigging practice

Turnback length

The length of the dead end of the rope that is folded back alongside the live part when a rope eye is made with clips. Too short a turnback means too little rope for the clips to grip, and the end can pull through.

Live end and dead end

In a rope eye, the live end is the part that carries the load; the dead end is the short length that is folded back and clamped. Clips are oriented by reference to these two — the saddle always goes on the live end.

Seating / bedding in

The settling that occurs in a rope termination or a threaded assembly when it is first loaded: strands compact, and nuts lose part of their preload. This is why torque must be re-checked after first load.

Definitions are the general meanings used in lifting and rigging practice. Where a contract or a national regulation applies, that instrument governs.

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