Crane hook blocks · Block type and sheave count against capacity and reeving, rope loading, hook material and latch, sheave guards, and hook inspection and discard limits
A crane hook block (bottom block) is the assembly of hook, swivel, bearing, sheaves, pins and frame that hangs in the hoist ropes and carries the load. Fix three things before ordering: the rated capacity, crane type and reeving (number of rope falls and sheaves), the hook type, material and latch the loads need, and the inspection, test and documentation rules the crane operates under.
Hook blocks for overhead, gantry, jib, port and deck cranes, with single, ramshorn, laminated, rotating or explosion-proof hooks. Oilfield drilling hook and travelling blocks, loose crane hooks without a block, chain-hoist bottom hooks sold alone, shackles and slings are outside this page; material-handling cranes have their own page.
01
US OSHA's overhead and gantry crane standard, 29 CFR 1910.179, defines the load block as the assembly of hook or shackle, swivel, bearing, sheaves, pins and frame suspended by the hoisting rope. It requires that the rated load divided by the number of rope parts not exceed 20% of the rope's nominal breaking strength, that at least two wraps remain on the drum with the hook at its lowest position, and that hooks meet the maker's recommendations and not be overloaded. [1]
A linked crane maker describes five hook-block types: single-hook blocks with 1–4 sheave grooves, which it places below 80 t; ramshorn blocks with dual lifting points and 4–8 sheaves for 50–100 t and larger cranes; laminated blocks riveted from steel plates, used on large cranes and for ladle handling; rotating blocks with 360° positioning; and explosion-proof blocks with spark-proof materials. It cites forged hooks quenched and tempered, a DG35CrMo single hook for a gantry crane, a 30Cr2Ni2Mo custom 50 t hook, Q345 plates for laminated ladle hooks, safety latches, ultrasonic testing and tensile testing. [2]
Editorial calculation: a 20 t block reeved with 4 rope parts puts about 49 kN on each part (20,000 kg × 9.81 m/s² ÷ 4). Under the 20% rule, the rope's nominal breaking strength must be at least about 245 kN (49 ÷ 0.20). More parts lower the load per rope and need more sheaves in the block. [1]
Give the supplier the crane type and model, rated capacity and duty, reeving (rope parts and sheave count), rope diameter and sheave groove size, hook type (single, ramshorn, laminated, rotating), hook material and latch, lifting height and drum details, environment (outdoor, hot metal, explosion hazard), inspection documents and quantity.
02
OSHA 1910.179 requires sheave grooves to be smooth and free of defects that could damage rope, close-fitting guards on sheaves whose ropes can be momentarily unloaded, and close-fitting guards on bottom-block sheaves so that ropes cannot foul when the block lies on the ground with ropes slack. [1]
Hooks must be visually inspected daily for deformation or cracks, with a monthly certified record of date, inspector and hook serial number. Hooks with cracks, with throat opening more than 15% above normal or twisted more than 10° from the plane of the unbent hook must be discarded; "repairs by welding or reshaping are not generally recommended". Load tests must not exceed 125% of rated load unless the maker recommends otherwise. [1]
Editorial calculation: a hook with a 60 mm throat opening when new reaches the 15% discard threshold at 69 mm (60 × 1.15). Record the as-new throat opening, or mark two gauge points, at delivery so that later measurements have a reference. [1]
Linked suppliers list crane hook blocks for overhead and gantry cranes, bottom hook assemblies for chain hoists, crane sheaves and heavy-lift hook blocks. [3] [4]
03
The listings reviewed cover single and ramshorn hook blocks, laminated ladle hooks, rotating and explosion-proof blocks, and sheaves and hooks as spares; ask each for the rated capacity, proof-test certificate, hook material certificate and ultrasonic test report.
04
OSHA 1910.179 defines the load block as hook or shackle, swivel, bearing, sheaves, pins and frame, and requires close-fitting guards on bottom-block sheaves. [1]
| Part | Role | Fix in the order |
|---|---|---|
| Hook | Carries the load; single, ramshorn or laminated. [2] | Type; material; latch. |
| Swivel and thrust bearing | Lets the hook rotate. [1] [2] | Bearing; rotation. |
| Sheaves | Reeve the rope parts. [1] [2] | Number; groove size. |
| Sheave guards | Keep slack rope in grooves. [1] | Guards. |
| Side plates and pins | Frame of the block. [1] | Material; pin size. |
| Crosshead and nut | Hold hook in block. [2] | Locking; caps. |
05
The as-new hook throat opening is worth recording here, because OSHA's 15% discard limit is measured against it. [1]
| Field | What it means and published values | Ask the supplier for |
|---|---|---|
| Rated Capacity (t) | Single below 80 t; ramshorn 50–100 t and above. [2] | Capacity; duty class. |
| Working Load Limit (t) | Maximum load in service. [1] | WLL marking. |
| Hook Opening (mm) | Discard at +15% over normal. [1] | As-new throat opening. |
| Hook material | Examples DG35CrMo, 30Cr2Ni2Mo, Q345 plates. [2] | Grade; certificate. |
| Safety Factor | Rope: rated load per part ≤20% of breaking strength. [1] | Hook and rope factors. |
| Operating Temperature (°C) | Ambient or hot-metal service. [2] | Range. |
| Pulley Diameter (mm) | Sheave size for the rope. | Diameter; groove. |
| Rope Diameter (mm) | Matched to sheaves and drum. | Diameter. |
| Weight (kg) | Block weight adds to hoisted load. | Weight. |
| Dimension (L×W×H) (mm) | Envelope and headroom. | Drawing. |
| Surface Treatment | Anti-corrosion paint. [2] | Coating. |
06
Paste it into your enquiry below or into an email to a maker, then replace every bracket.
Crane: [type; model; capacity; duty] Reeving: [rope parts; sheaves] Rope: [diameter; construction] Hook: [single; ramshorn; laminated; rotating; latch] Material: [grade; certificates] Environment: [outdoor; hot metal; explosion hazard] Tests: [proof load; UT; documents] Quantity: [per crane]
4 companies list this product among what they make. Company figures are quoted from each company's own website; every card states where the relationship came from.
Lists single, ramshorn, laminated, rotating and explosion-proof crane hook blocks with forged, quenched-and-tempered hooks.
Product scope checked 2026-10-11
Lists crane hooks, crane hook blocks and crane sheaves.
Product scope checked 2026-10-11
Lists crane hooks, automatic overhead crane hooks and bottom hook assemblies for chain hoists.
Product scope checked 2026-10-11
Lists crane hook blocks for heavy lifting alongside its cranes.
Product scope checked 2026-10-11
Explore company information and manufacturing capabilities, then discuss the scope of your project with a relevant supplier.
OSHA 1910.179 requires discard for cracks, throat opening over 15% above normal or twist over 10°. [1]
OSHA 1910.179 limits rated load per rope part to 20% of the rope's nominal breaking strength. [1]
OSHA 1910.179 caps test loads at 125% of rated load unless the maker recommends otherwise. [1]
One crane maker lists ramshorn blocks with 4–8 sheaves for 50–100 t and larger cranes. [2]
Sources checked 2026-10-12. OSHA 29 CFR 1910.179 is the US federal standard for overhead and gantry cranes; DGCRANE, KSCRANE and MAGICART are linked crane makers publishing hook block types and materials.
Ask for use case, specification boundaries, supplier type, and RFQ preparation information for this product.
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