Industrial buyers across SADC need to understand splicing trade-offs: Flemish eyes and swaged sleeves deliver maximum strength and redundancy for wire rope; brummel and deep-bury methods suit synthetic fibres; thimbles protect eye geometry. This guide covers efficiency ratings, inspection criteria, and when to splice versus swage.

Manufacturing 10 July 2026 • 11 min read

Proper splicing is not optional. A correctly executed splice retains 85-100% of rope strength, while a knot can reduce capacity by 50-80%. Choosing the right technique for your fibre type, load class, and environment directly affects safety and lifecycle cost. Industrial buyers must specify splicing method at procurement, verify execution, and establish inspection cadence.

What is a rope splice and why it matters

A splice is a permanent or semi-permanent termination created by weaving, burying, or interlocking rope or wire strands. Unlike a knot, which creates stress concentration and can slip, a splice distributes load evenly across the full cross-section of the material. Splicing is the preferred rope termination method because, in most cases, it maintains 100% of the specified rope strength, while knots can significantly decrease a rope's strength. Splices are used to form eyes (loops) for attachment to shackles, hooks, and rigging hardware. The choice of splice technique depends on four factors: fibre type (natural, synthetic, or wire), rope construction (stranded, braided, or double-braided), load requirements, and maintenance accessibility.

Flemish eye splices for wire rope

The Flemish eye is the most common type of wire rope eye sling. It is made by opening the wire rope's individual strands into two parts, then looping the two strands in opposite directions and laying them back together to create an eye shape at the end of the wire rope. This traditional method creates redundancy: if the swaged ferrule fails, the mechanically interwoven strands can still carry load. A carbon steel sleeve is placed over the splice and swaged under enormous pressure, creating a secure connection that traps the wire ends and will not come off even if it cracks or deforms.

Flemish eyes are typically preformed with 6x19 or 6x37 Independent Wire Rope Core (IWRC). Once the eye shape is formed, the rope is fitted with a carbon-steel sleeve, then fed into a hydraulic machine called a swager that helps form and fit the sleeve in place. The combination of mechanical splice plus ferrule swage produces the highest efficiency and safest outcome for lifting operations.

Thanks to its splicing method, the Flemish eye is the most efficient and economical wire rope eye type available. Additionally, if there were any malfunction or failure with the carbon-steel sleeve, the Flemish eye could potentially still reach its working load limit, giving you enough time to replace the damaged wire rope sling.

Synthetic fibre splicing: brummel, deep-bury, and Class III

Synthetic fibres (polyester, nylon, polypropylene, UHMWPE, aramid, Vectran) require different splicing techniques than natural rope or wire because of their low friction and high stretch characteristics. Five tucks are necessary for synthetic fibres, compared to three for natural fibres.

Deep-bury splice (Class III): The strongest method for synthetic rope. Strands are separated, tapered progressively, and the tail is buried back into the rope body for a length of 50-70 rope diameters. The buried eye splice achieves the effective 100% breaking strength of the rope. Tapers are often stitched with a lock stitch to prevent slipping under zero load, though stitching is buried inside the splice and does not carry load once tension is applied. This method is preferred for high-tension synthetic winch lines and lifting applications where permanent connection is acceptable. Deep bury is simpler and stronger, retaining 95% strength, but creates a permanent connection.

Brummel lock splice: Designed for hollow-braided and single-braided synthetics. A Brummel Eye Splice rope termination includes a double-braided portion of hollow-braided rope ending in a closed loop, with an outer braid portion and inner braid portion concentric with each other. The Brummel Eye Splice takes advantage of the tension-contraction coupling of hollow-braided rope construction to provide sufficient strength. In a Brummel splice the line is woven through the weave of the Dyneema rather than passed up the center of the core. Two passes create a lock. Brummel lock uses interlocking loops that can be disassembled if needed but requires more skill and typically retains 85-90% strength. The main advantage is reversibility, making it suitable for applications requiring equipment redeployment or rope rotation.

Bury depth and fibre specifics: DSM advises using 60 times the diameter for coated Dyneema and 100 times the diameter for uncoated Dyneema. For 6mm coated rope, this would mean 36 cm. For single braids, it is best to use a Brummel splice with a long tapered tail (at least 400mm long is necessary). For double braids, it is best to use a double braid UHMWPE eye splice. High-performance core fibres (Dyneema, Vectran, aramid) require longer buries than polyester or nylon because they transmit load primarily through the core, not the cover.

Thimbles: purpose, sizing, and corrosion risk

A thimble is a teardrop or oval-shaped metal insert placed inside the eye of a splice to protect the rope and maintain eye geometry. A rope thimble can be inserted in the eye to prevent chafing if the eye is to be permanently attached to a fixture, such as when attaching a rope to a chain. Thimbles protect the wire rope from crushing and wear and tear, resulting in an extended lifespan of the sling. Thimbles also prevent sharp bending that concentrates stress and reduces rope life. Thimbles are essential for winch applications because they protect against abrasion and crushing at the connection point, especially critical for repeated loading cycles. Thimbles also maintain proper bend radius, preventing the rope from flattening under load and stressing fibres unevenly.

Thimble materials and marine corrosion: In offshore and marine environments, thimble material selection is critical. Stainless steel thimbles are preferred for galvanised wire rope to prevent galvanic corrosion. Galvanic corrosion occurs from contact between dissimilar metals, such as carbon steel hooks on stainless wire slings, creating an electrochemical cell that corrodes the less noble metal. All fittings must match the sling material grade in marine assemblies. LEEA guidance states that any marine lifting sling showing visible corrosion, pitting, or discolouration on metal components requires withdrawal from service and competent person inspection before reuse. For SADC port operations and mining sites with salt spray or humidity exposure, specifying matched-grade ferrules and thimbles is not optional.

Heavy-duty thimbles withstand the working load conditions of slings, but when severely overloaded they will noticeably stretch, serving as a visible warning of abuse. This is a safety feature: overstretched thimbles signal that the sling has been overloaded and requires withdrawal from service.

Splice efficiency ratings and strength retention

Splice efficiencies are measured as the actual breaking strength of a spliced termination divided by the actual breaking strength of the rope. This efficiency will change from splice to splice because of the many variable factors involved in producing the splice. Efficiency is not uniform; it depends on fibre type, construction, splice length, and execution quality. Industrial buyers should request splice efficiency certificates from manufacturers and compare across suppliers.

Wire rope splices: Flemish mechanical splices typically achieve 90-95% efficiency. Serving or wrapping of wire rope sling splices does not affect the splicing efficiencies nor rated capacities. Such servings are optional, although unserved splices are preferred because they permit visual inspection of the spliced area. This is a procurement consideration: unserved (bare) splices are easier to inspect for strand separation or distortion.

Synthetic fibre splices: Deep-bury splices in high-performance synthetics achieve 95-100%. Brummel splices achieve 85-90% and should be derated if used in critical load paths. The difference between a secure splice and a weak knot is that properly executed splices maintain nearly full rope capacity, while knots in synthetic lines can reduce strength by 50-80%. This is why OSHA and ASME standards explicitly prohibit knots for load-bearing rope terminations.

Inspection criteria and discard thresholds

All spliced slings must be inspected before initial use and at regular intervals thereafter. It is mandatory to follow ISO4309 safety requirements for rope inspection. The competent person must be aware of how they are performing the inspection, because they must keep themselves and the plant safe by following ISO4309 regulation to be in compliance with the correct inspection procedure. For wire rope slings:

A wire rope sling must be immediately discarded if 10 or more randomly distributed broken wires are present in one rope lay, or 5 broken wires appear in one strand in one rope lay. Reduction of the nominal rope diameter by more than 1/32" for diameters up to 5/16", or 1/16" for diameters up to 1/2" indicates wear. Kinking, crushing, or bird caging (where outer strands flare out from the core) indicates distortion that requires immediate removal from service. Cracks, excessive wear, or distortion in hooks, rings, or eye splices also requires removal.

For synthetic fibre slings: After each use, inspect for cut strands, compression, pulled strands, melted or glazed fibre, discolouration, degradation, inconsistent diameter and abrasion. Glossy or glazed areas, inconsistencies in texture, and stiffness are indicators that the rope has been subjected to elevated temperatures, has embedded grit, or has been subjected to shock loading and possible loss of strength. Synthetic ropes can mask internal damage, so regular competent-person inspection is essential.

Splice versus swage: when to choose each

Mechanical splice (Flemish eye for wire rope, deep-bury or brummel for synthetics): Choose splicing when you need mechanical redundancy, maximum strength retention, or the ability to inspect the splice visually. Splicing is labour-intensive and requires skilled riggers, but the result is permanent, highly efficient, and does not require special tooling to verify (visual and tactile inspection suffices). Spliced slings are preferred in critical lifting applications: offshore, crane rigging, demolition, and rescue operations.

Swaged ferrule (on wire rope or some synthetics): The swage process involves unlaying the wire rope at each end and then relaying the strands in opposite directions to form the eye, with a carbon steel sleeve then placed over the splice and swaged (pressed) under enormous pressure. The Flemish eye is the most efficient and economical wire rope eye type available. However, in a mechanical splice (loop-back) method, the rope end is simply bent back to form the eye and held in place with a swaged sleeve, and unlike the Flemish Eye, the strands are not interwoven before swaging. While faster to fabricate, a mechanical splice does not provide the same strength or level of safety. The swage process requires calibrated hydraulic equipment and strict process control; if the ferrule is under-swaged, it can slip. The Flemish splice combined with a swage provides redundancy: if the ferrule slips, the interwovenstrands still hold.

For all eye splices, the eye shall be sufficiently large to provide an included angle of not greater than 60 degrees at the splice when the eye is placed over the load or support. This requirement applies regardless of splicing method and is verified during inspection and proof-testing.

Procurement notes for SADC industrial operators

SADC mining and maritime operations depend on reliable lifting slings. When specifying slings, procurement teams should include explicit splicing method and efficiency requirements in RFQs. Request split between Flemish eye (wire rope, maximum strength) and deep-bury or brummel (synthetics). Verify that all ferrules and thimbles are matched-grade stainless steel or galvanised carbon steel (never carbon steel on galvanised rope, or vice versa). Proof-test certificates must accompany all slings to ASME B30.9 or equivalent SANS standard; do not accept slings without test data.

Lead times for custom-spliced slings in the SADC region can be 4-8 weeks depending on rope diameter and volume. Standard stock (8-13mm wire rope slings with Flemish eyes) is usually available within 2-3 weeks. Synthetic rope slings require longer buries and are often imported rather than locally spliced; verify supplier capability before committing to timeline. Maintenance access in mines and ports requires unserved (bare) Flemish eyes for visual inspection; specify this explicitly rather than assuming.

For coastal operations (Walvis Bay, Durban, Maputo), specify galvanised or stainless fittings and arrange for annual competent-person inspection with corrosion assessment. A 10% diameter loss from corrosion reduces tensile capacity by approximately 19%, so slings can lose working load capacity without visible breakage. Budget for replacement on a 3-5 year cycle in high-corrosion environments.

About the Author
	Andre Klynsmith Co-Shareholder · Technology & Operations Andre's expertise spans technology, e-commerce, AI integration, and industrial procurement systems, driving Marine Ropes' digital transformation across Southern Africa. salesdesk@marine-ropes.com | marine-ropes.com