8.3 Rigging Hardware, Shackles, Hooks & Below-the-Hook Lifting Devices

Quick Answer: Rigging hardware connects lifting slings to the crane hook and the load. Governed by ASME B30.26 (Rigging Hardware), ASME B30.10 (Hooks), and ASME B30.20 (Below-the-Hook Lifting Devices), fittings must be permanently marked with manufacturer identification and the rated load, or Working Load Limit (WLL). Screw pin shackles are standard for pick-and-place lifts, while bolt-type safety shackles (bolt, nut, cotter pin) are the preferred choice for long-term rigging or where line contact could rotate the pin. Loading shackles at angles reduces their capacity (typically 70% at 45° and 50% at 90°, per the manufacturer's chart), and loading across the jaws is not permitted. Hooks must be rejected if throat opening expands by >5% (or 1/4 in), if twist exceeds 10°, or if saddle wear exceeds 10%. Shouldered eyebolts lose 70% capacity at 45°, and unshouldered eyebolts are prohibited for angular pulls.

While slings absorb and transmit tensile hoisting forces, the mechanical reliability of the entire rigging system depends upon the connectors: shackles, hooks, eyebolts, turnbuckles and engineered lifting beams. 230 CMR 6.01(3) adopts ASME B30.10-2014 (hooks), B30.20-2018 (below-the-hook devices) and B30.26-2015 (rigging hardware), and OSHA 1926.251 requires rigging to be inspected each shift and removed from service when defective. Failure of a single hardware component can release the load.

1. Rigging Shackles (ASME B30.26): Types, Assembly & Loading Dynamics

Shackles are the universal primary connector in crane rigging. Lifting shackles are usually forged carbon steel (often with alloy pins) or quenched-and-tempered alloy steel. ASME B30.26 requires each shackle body to be marked with the manufacturer's name or trademark, the rated load and the size.

Screw Pin vs. Bolt-Type Safety Shackles

1. Screw Pin Shackles:
   • Design: The pin features external machine threads that screw directly into the tapped ear of the shackle body.
   • Field Application: Designed for temporary, pick-and-place hoisting operations where rigging is frequently attached and disassembled.
   • Assembly Rules: Tighten the pin until its shoulder is fully seated against the shackle ear, as the manufacturer's instructions require. Do not back it off. If the pin could rotate or work loose in service, use a bolt-type shackle, or secure the screw pin as the manufacturer allows (for example, seizing wire through the pin eye).
2. Bolt-Type Safety Shackles (Bolt, Nut & Cotter Pin):
   • Design: Features an unthreaded bolt that passes completely through both unthreaded shackle ears, secured on the exterior by a heavy hexagonal nut and a split steel cotter pin.
   • Preferred Applications: Bolt-type safety shackles are the preferred choice for permanent or semi-permanent rigging, long-term suspended loads, submerged lifts, and any operation where a running sling or tagline could roll across the shackle pin. In a choker hitch, a sliding wire rope eye rolling across a screw pin can back the pin out, dropping the load; a bolt-type shackle completely eliminates this hazard.

Shackle Loading Geometry & Angular Capacity Derating

Shackle rated loads assume an in-line pull through the centerline of the bow and pin. ASME B30.26 requires side loading to be handled per the manufacturer's guidance, and a typical manufacturer side-load reduction chart for screw-pin and bolt-type shackles looks like this:

2. Crane Hoist Hooks (ASME B30.10): Inspection & Removal Criteria

Crane hoist hooks and rigging attachment hooks are forged from alloy steel and engineered to yield gradually under extreme overload rather than snap in brittle failure. OSHA 29 CFR 1926.1412(d)(1)(v) requires hooks and latches to be inspected each shift for deformation, cracks, excessive wear and chemical or heat damage, and ASME B30.10 sets the measured removal criteria.

Safety Latch Operational Mandates

OSHA 1926.1433(d)(4) requires crane hooks to be equipped with latches that close the throat opening, unless a qualified person determines that hoisting without latches is safer and load routes keep workers out of the fall zone. For personnel hoisting, hooks must be of a type that closes and locks (OSHA 1926.1431(g); 230 CMR 6.09(6)(e)). The safety latch prevents slings, rings, and shackles from jumping out of the hook bowl when the hoist line goes slack or during dynamic load movement. Latches must never be tied open, cut, or modified. Crucially, safety latches are not load-bearing structures; if a sling eye rests directly against the latch rather than seating firmly in the bottom saddle of the hook, the latch will instantly shear, releasing the load.

Critical Hook Removal Rejection Thresholds

Under ASME B30.10, a hook must be removed from service if any of the following conditions is found, unless the manufacturer's criteria are stricter:

1. Throat Opening Expansion: Any increase in the hook throat opening exceeding 5% of the original manufactured dimension, or 1/4 inch (6.4 mm), whichever is less. (Riggers verify this during periodic inspections using caliper measurements between manufacturer-stamped prick-punch center marks).
2. Out-of-Plane Hook Twist: Any twist or bend exceeding 10 degrees out of the original plane of the unbent hook body.
3. Saddle / Bowl Wear: Any wear exceeding 10% of the original cross-sectional dimension of the hook bowl, saddle, or load-bearing shank pin hole.
4. Surface Cracks, Gouges, or Sharp Notches: Any visible crack, severe gouge, or sharp transverse notch. Minor longitudinal nicks may be ground out smooth by a qualified technician provided the remaining cross-sectional dimension does not fall below the 10% wear limit.
5. Heat Damage or Field Welding: Any sign of excessive heat exposure, electric arc strikes from welding cables, or unauthorized field welding. Field welding, heating, or brazing on any crane hook is strictly prohibited because heat alters the metallurgical quench-and-temper structure and causes immediate embrittlement.

3. Eyebolts & Swivel Hoist Rings (ASME B30.26): Angular Shear Risks

Eyebolts provide threaded pick points on machinery, motor casings, and equipment skids. However, severe rigging accidents frequently occur when riggers fail to distinguish between shouldered and unshouldered eyebolt designs.

Unshouldered (Plain) Eyebolts: Pure Vertical Pulls Only

• Mechanical Limitation: Plain, unshouldered eyebolts feature a threaded shank that transitions directly into the eye ring without a machined collar or shoulder.
• Absolute Rule: Plain unshouldered eyebolts are approved strictly and exclusively for pure vertical in-line pulls ($0^\circ$ from the shank axis / $90^\circ$ to the load surface).
• Failure Mechanism: If an unshouldered eyebolt is subjected to an angular pull (even as shallow as $15^\circ$), the bending moment acts across the thread root, concentrating stress there, which can bend the shank and snap it off flush with the load face.

Shouldered Eyebolts: Permitted Angular Pulls & Severe Deratings

• Mechanical Design: Shouldered eyebolts incorporate a heavy, machined integral collar that seats flush against the machined load surface, transferring transverse bending loads into the load body.
• Installation Requirements: Shouldered eyebolts must be screwed down until the shoulder seats fully and tight against the mounting surface, following the manufacturer's instructions. Where the eye must be turned to line up with the pull, manufacturers allow steel washers or shims of limited thickness under the shoulder. The plane of the eye must be in line with the direction of the sling pull. Pulling across the eye plane will bend and break the eye.
• Angular Reduction (typical manufacturer chart): Even with proper seating and alignment, angular loading sharply reduces the working load limit of shouldered eyebolts. Always use the manufacturer's chart for the eyebolt in hand:

For angles between the listed values, use the manufacturer's chart for the eyebolt in hand.

Swivel Hoist Rings: The Engineered Modern Solution

Because shouldered eyebolts lose 70% of their lifting capacity at a standard $45^\circ$ horizontal sling angle, modern rigging engineering utilizes swivel hoist rings. Swivel hoist rings feature a central mounting bolt that torques into the load, allowing the bail to pivot 180 degrees and the base to swivel 360 degrees. When torqued to manufacturer specifications, swivel hoist rings maintain 100% of their rated Working Load Limit at all operating angles.

4. Below-the-Hook Lifting Devices: Spreader Bars vs. Equalizer Beams (ASME B30.20)

Below-the-hook lifting devices are specialized structural assemblies engineered to handle loads that cannot be rigged safely with standard slings alone. Governed by ASME B30.20, these devices fall into two primary mechanical categories:

Spreader Bars (Compression Beams)

• Mechanical Function: A spreader bar consists of a rigid horizontal structural tube, pipe, or I-beam positioned between the upper rigging and the load. Two inclined upper sling legs connect the crane hook to the ends of the spreader bar, while two lower sling legs drop straight down from the bar ends to connect to the load pick points.
• Engineering Purpose: The spreader bar's primary function is to absorb all inward horizontal compressive vector forces generated by the inclined upper slings. By taking the horizontal compression through the structural beam itself, the lower sling legs hang pure vertical ($90^\circ$) to the load.
• Ideal Applications: Long structural steel beams, fragile sheet metal assemblies, thin-walled storage tanks, pipes, and wide wooden roof trusses that would crush, buckle, or deform under the inward compressive force of standard inclined slings.

Equalizer Beams (Tandem & Center-of-Gravity Balancers)

• Mechanical Function: An equalizer beam is a heavy structural beam designed to distribute and balance load forces evenly between two crane hooks (in tandem lifting) or between multiple pick points on an asymmetrical load.
• Engineering Purpose: Equalizer beams ensure that each pick point or crane maintains its predetermined share of the load, even if one hoist line speeds up slightly or if the load oscillates during slewing. Equalizer beams frequently feature adjustable pin shackles along their bottom flange to accommodate varying Centers of Gravity.

ASME B30.20 Structural Marking & Proof-Testing Standards

Under ASME B30.20, below-the-hook lifting devices are subject to rigorous manufacturing, testing, and operational rules:

1. Design Factors: ASME B30.20 requires below-the-hook devices to be designed to ASME BTH-1, which uses Design Category A (design factor 2.0 on yield, for predictable, controlled service) and Design Category B (design factor 3.0, for less predictable service). The category is marked on the device.
2. Load Testing: ASME B30.20 calls for new, altered or repaired lifters to be load tested and inspected before use, by or under the direction of a qualified person, at 125% of the rated load unless the manufacturer or a qualified person specifies otherwise. OSHA 1926.251(a)(4) makes a 125% proof test mandatory for custom-designed lifting accessories.
3. Permanent Nameplate Data: The device must display a permanent, durable metal identification plate specifying:
   • Manufacturer's name and contact information,
   • Unique serial or unit identification number,
   • Lifter Dead Weight (which must be deducted from the crane's gross rated load chart capacity as rigging tackle!),
   • Rated Working Load Limit (WLL),
   • Design category and service class where required by ASME BTH-1.

5. Comprehensive Hardware Inspection Rejection Checklist

The following reference table summarizes the definitive removal criteria for rigging hardware under ASME B30 standards: