Rigging hardware: shackles, hooks, eyebolts and wire rope terminations

The rated load of a shackle, hook or eyebolt assumes it is loaded in line, in the direction the maker designed it for. Load it any other way and the capacity falls, sometimes by more than half.

Shackles

• Bow (anchor) shackles accept loads at an angle and several sling eyes in the bow. Dee (chain) shackles are for straight, in-line pulls only.
• Pin types: screw-pin for temporary rigging that is removed after the lift; safety (bolt, nut and split pin) for long-term or permanent rigging, or wherever the pin could turn under load.
• Side loading (load applied at an angle to the shackle’s plane) reduces capacity. A typical manufacturer’s reduction for screw-pin and bolt-type bow shackles is:

• Put the sling on the bow and the pin through the lug or hook. Never let a moving sling run over the pin, which can unscrew it.
• With two sling legs in one bow, keep the included angle within the maker’s limit, commonly 120°.
• Never replace a shackle pin with a bolt. Never use a shackle with a bent pin, a spread or worn bow, or illegible markings.
• The shackle must suit the lug: the pin should be a close fit in the lug hole, and the jaw wide enough for the lug thickness plus any cheek plates. Spacers or washers can centre a narrow lug.

Hooks

• The rated load applies only when the load sits in the bowl (saddle) of the hook. Tip loading, with the load on the point, drastically reduces capacity and is not allowed.
• Every lifting hook should have a working safety latch, unless a documented exception applies (for example foundry work).
• Remove a hook from service (ASME B30.10) for any of these: cracks; an increase in throat opening of more than 5% (not exceeding 6 mm / ¼ in) or as the maker specifies; twist of more than 10° from the plane of the unbent hook; wear of more than 10% of the original section dimension; or heat damage, welding or unauthorised repair.
• Do not put two sling eyes on top of each other in a hook. Use a shackle or master link to collect several legs.

Eyebolts and lifting points

• Plain (non-shoulder) eyebolts are for vertical, in-line loads only.
• Shoulder eyebolts may be loaded at an angle, but only in the plane of the eye. Capacity drops sharply: a typical maker’s rating is about 30% at 45° and 25% at 90° from vertical. Seat the shoulder fully. Use a shim washer to bring the eye into the plane of the pull, never a part-tightened thread.
• For angled multi-leg lifts, use swivel hoist rings rated for the angle, which turn to face the load.
• Welded lugs and padeyes must be designed for the actual sling direction, both in plane and out of plane. They should be fabricated and inspected to the drawing and, where the procedure requires, load tested or checked by NDT. A lug designed for a vertical pull is not automatically good for a 45° pull.

Wire rope terminations

An end termination is often weaker than the rope itself. Typical efficiencies (percentage of the rope’s minimum breaking force) are:

Wire rope grips are not normally acceptable for making lifting slings. Use them only where the governing standard and the rope maker allow it, such as for some temporary guys and tag lines.

Before each use

• Check the WLL marking, the identification and the thorough examination record. Under LOLER, accessories need a thorough examination at least every 6 months, or as the examination scheme requires.
• Look for distortion, cracks, wear, nicks, corrosion, heat marks and missing pins or latches.
• Check that the hardware is compatible: shackle to lug, sling eye to shackle bow, hook to master link.

Screening a plate lifting lug

Lugs welded to equipment are designed by an engineer to ASME BTH-1 or an equivalent standard, but a rigger or planner should be able to check that a lug is in the right range for the load. Three simple stresses give a quick screen:

Net tension σ_t = P ÷ ((w − d_h) × t)    Bearing σ_b = P ÷ (d_p × t)    Tear-out τ = P ÷ (2 × (R − d_h/2) × t)
w = plate width at the hole, d_h = hole diameter, d_p = pin diameter, t = plate thickness, R = distance from hole centre to the plate edge in line with the load.

Example. A lug in S355 steel carries P = 20 t (196 kN) in its plane. Plate 30 mm thick, 160 mm wide at the hole, hole 52 mm for a 50 mm shackle pin, R = 70 mm.

• Net tension: 196,200 ÷ ((160 − 52) × 30) = 196,200 ÷ 3,240 = 60.6 MPa.
• Bearing: 196,200 ÷ (50 × 30) = 130.8 MPa.
• Tear-out: 196,200 ÷ (2 × (70 − 26) × 30) = 196,200 ÷ 2,640 = 74.3 MPa.

All three are modest for S355. The design check itself uses the BTH-1 pin-connected plate equations, which allow for stress concentration at the hole, with a design factor N_d of 2.0 for Design Category A or 3.0 for Category B, plus the weld to the structure, the structure behind the lug, and any out-of-plane load. Treat the screen as a sense check, not as the design.

Shackle and lug fit

• Pin and hole. The hole should be only slightly larger than the pin. A large clearance concentrates the bearing at the top of the hole and bends the pin.
• Lug thickness and jaw width. The lug should fill a good part of the shackle jaw (often 60–75% or more). A thin lug in a wide shackle lets the pin bend; use cheek plates on the lug or spacers, as the designer specifies.
• Crown clearance. The plate edge above the hole must not touch the inside of the shackle bow or body.
• Alignment. Orient the lug in the direction of the sling, or design it for the out-of-plane component. A lug bent sideways is far weaker than in its plane.

Side loading and angle reductions

Shackles are rated for a load in line with the shackle’s centreline. When two slings share one shackle at an angle, or a single sling pulls across the bow, the capacity falls. Typical published values for screw-pin and bolt-type shackles are 100% in line, 70% at 45° and 50% at 90°. A 17 t shackle pulled at 45° is good for about 11.9 t; at 90°, 8.5 t.

Eyebolts are worse. A shoulder eyebolt loaded at 45° to its axis, in the plane of the eye, is typically limited to about 30% of its rating; at 90°, about 25%. A 5 t eyebolt at 45° carries about 1.5 t. Plain (non-shoulder) eyebolts must only be loaded in line with the shank. If angular loads are needed, use swivel hoist rings rated for the angle, or design lift points instead.

Wire rope terminations

Every termination is weaker than the rope. Typical efficiencies, as a percentage of the rope’s minimum breaking force, are:

Wire rope clips

• Fit the U-bolt on the dead (tail) end and the saddle on the live end on every clip: “never saddle a dead horse”.
• Use the number of clips, the turnback length and the nut torque in the clip maker’s table for that rope size. Space the clips as the table states.
• Tighten in the order given, load the rope, then retighten to the full torque. Check again at regular intervals.
• Do not use clips for slings made for general lifting. Under BS EN 13414-1 and ASME B30.9, slings use pressed ferrules, hand splices or sockets.

Wedge sockets

• The live end must run straight out of the socket in line with the pin. If the live end is on the wrong side, the rope bends sharply and the wedge can pull out.
• Leave a tail long enough for the maker’s rule (commonly at least 6 rope diameters and at least 150 mm).
• Secure the tail with a clip to a short separate piece of rope or by the maker’s method. Never clip the tail to the live rope.
• Seat the wedge with a light load before full service.

Hooks: removal criteria

• Throat opening increased by more than 5% (ASME B30.10 also limits the increase to 6 mm, or as the maker states), or a missing or damaged latch where a latch is required.
• Twist of more than 10° from the plane of the unbent hook.
• Wear of more than 10% of the original section, or any crack, nick or gouge.
• Any sign of heat damage, weld repair or unauthorised modification.

Load the hook in its bowl (the saddle), never on the tip. Two sling eyes on one hook should sit with an included angle of 90° or less, otherwise put both eyes in a shackle or use a master link.

Common mistakes

• Replacing a lost shackle pin with a bolt. A bolt is not a pin and has a different strength and fit.
• Letting a screw-pin shackle unscrew under a rotating load. Use a bolt, nut and split pin shackle for long-term or rotating rigging.
• Pulling a sling across a shackle pin, so that the pin can rotate and unscrew. Put the sling eye on the pin and the lug or other sling in the bow, or as the maker allows.
• Using an eyebolt at an angle without checking its reduced rating, or screwing it in only part way.
• Lifting on a lug fitted for transport or tie-down, which may only be designed for a lashing force.

Self-check questions

General guidance only. It does not replace the manufacturer's data, the applicable standards or the judgement of a competent person.

References

Technical references consulted for this chapter. The text and worked examples are original to LiftPlan Pro.

• Ronald G. Garby, IPT’s Crane and Rigging Training Manual: Mobile, EOT and Tower Cranes (IPT Publishing and Training).
• Rigging Handbook, 2nd edition (Bechtel Equipment Operations, 2002).
• ASME B30.9 Slings; ASME B30.26 Rigging Hardware; ASME B30.10 Hooks.

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