Drilling rig crown blocks · rated hook load, number of sheaves and reeving, sheave diameter against wireline size, fast-line and sand-line sheaves, bearings, groove hardening and API 4F and 8C
A crown block is the fixed set of sheaves mounted on beams at the top of a drilling mast or derrick; the drilling line runs over its sheaves and down through the travelling block, so together they multiply the drawworks' pull to lift the drill string. Ask three things first: what hook load it is rated for, how many sheaves and what reeving it gives with the travelling block, and what sheave diameter and groove suit your wireline size.
Crown blocks for land and mobile drilling rigs and workover rigs, built to API Spec 4F and 8C, including main, fast-line, sand-line and auxiliary sheaves. Travelling blocks, hooks and swivels, and individual sheaves or bearings sold alone are outside this page except where compared.
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01
OSHA's oil and gas glossary describes the crown block as an assembly of sheaves or pulleys mounted on beams at the top of the derrick, over which the drilling line runs down to the hoisting drum, and the travelling block as the sheaves through which the line is reeved that move up and down in the mast. [1] Sovonex's crown block table runs from CB30 (300 kN, 4 sheaves) and CB90 (900 kN, 5 sheaves) to CB315 (3,150 kN, 7 sheaves) and CB450 (4,500 kN, 7 sheaves), built to API Spec 4F and 8C. [2]
ZPEC's skid-mounted rig table gives the matching hoisting system for each class: ZJ30 and ZJ40 with a 5 × 6 maximum reeving, ZJ50 and ZJ70 with 6 × 7, ZJ90 with 7 × 8, and drilling line of 29, 32, 35, 38 and 45 mm with travelling sheaves of 1,005, 1,120, 1,270, 1,524 and 1,524 mm respectively; its electric-rig table lists 12 lines for the 4,500 kN ZJ70. [3] A ZJ70/4500DZ equipment-limits sheet lists a TC450 crown block rated 4,500 kN with 7 main sheaves of 1,524 mm for 38 mm wire rope, and a drilling line with a minimum breaking force of 1,010 kN. [4]
Editorial calculation: a 6 × 7 system has 6 sheaves in the travelling block and 7 in the crown; with the line passing over the crown sheaves and around the travelling sheaves, 6 travelling sheaves give 2 × 6 = 12 lines supporting the block, the figure ZPEC lists for its ZJ70. At 4,500 kN that is 4,500 / 12 = 375 kN per line before sheave friction.
Give the supplier the rig class and mast, maximum hook load, reeving (lines strung), drilling line diameter and construction, sand-line and auxiliary winch lines, mast top dimensions and mounting, crown saver or bumper requirements, climate and corrosion protection, and API monogram and certification required.
02
Sovonex lists wireline and sheave sizes for each model, for example 24 mm line on 475 mm sheaves (CB30), 29 mm line on 1,005 mm sheaves (CB135, CB170), 35 mm on 1,270 mm (CB315) and 38 mm on 1,524 mm (CB450). It describes sheaves machined from an integral alloy steel body and heat treated against rim cracks, induction-hardened grooves to reduce wireline wear, each sheave on its own tapered roller bearings with a separate lubrication passage, sheaves and bearings interchangeable with its travelling blocks, a fast-line sheave, a sand-line sheave, auxiliary winch sheaves, a crown platform with handrails and a crown bumper. [2]
Editorial calculation: the sheave-to-line diameter ratio is 1,524 / 38 ≈ 40 for the 4,500 kN model and 1,005 / 29 ≈ 35 for the 1,350–1,700 kN models, but only 475 / 24 ≈ 20 for the smallest. Ask the supplier which minimum ratio its design follows for your wire rope and how groove radius matches the rope.
03
Suppliers linked to this page list crown blocks; each card links to the page reviewed.
Listings include API crown blocks with other rig components, crown blocks with travelling blocks, hooks and swivels, and crown blocks from oilfield equipment suppliers. Companies listing only crown block sheaves are hidden here as component suppliers. Ask each for hook load, sheave count and size, line size, bearings and API monogram.
04
This is a functional reference built from the sources cited; it is not one maker's specification.
| Part | Role | Fix in the order |
|---|---|---|
| Main sheaves | Carry the drilling line. [2] [4] | Number, diameter, groove. |
| Fast-line sheave | Leads line to the drawworks. [2] | Size. |
| Sand-line and auxiliary sheaves | Other winch lines. [2] | Number and size. |
| Bearings | Tapered roller per sheave. [2] | Type and lubrication. |
| Frame and beams | Mount on mast top. [1] | Fit to mast. |
| Platform and bumper | Access and protection. [2] | Handrails, bumper. |
05
A crown block quotation needs values for your rig. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.
| Field | What it means and published values | Ask the supplier for |
|---|---|---|
| Rated Load Capacity (kN) | Examples: 300–4,500 kN. [2] | Rating and API 8C. |
| Number of Sheaves | Examples: 4–7 main sheaves. [2] [4] | Main and auxiliary sheaves. |
| Sheave Diameter (mm) | Examples: 475–1,524 mm. [2] | Diameter. |
| Wireline Diameter (mm) | Examples: 24–38 mm. [2] [3] | Line size. |
| Working Load Limit (%) | Line loads. | Load per line. |
| Operating Temperature (°C) | Climate. | Range. |
| Material Grade | Alloy steel sheaves. [2] | Grades. |
| Weight (kg) | Mast top load. | Weight. |
| Overall Dimensions (L×W×H) (mm) | Example CB450: 3,407 × 2,722 × 2,856 mm. [2] | Dimensions. |
| Bearing Type | Tapered roller. [2] | Type. |
| Lubrication Method | Individual passages. [2] | Method. |
| Corrosion Protection | Coating. | System. |
06
Paste it into your enquiry below or into an email to a maker, then replace every bracket.
Rig: [class; mast type] Load: [hook load; lines strung] Line: [diameter; construction] Sheaves: [main; fast line; sand line; auxiliary] Mounting: [mast top dimensions] Certification: [API 4F; API 8C monogram]
These companies list crown blocks.
Lists API crown blocks with other rig components.
Product scope checked 2026-10-11
Lists crown blocks with travelling blocks, hooks and swivels.
Product scope checked 2026-10-11
Lists crown blocks among drilling rig equipment.
Product scope checked 2026-10-11
Lists a crown block among its equipment.
Product scope checked 2026-10-11
Explore company information and manufacturing capabilities, then discuss the scope of your project with a relevant supplier.
Sovonex's range runs from 4 to 7 main sheaves; ZPEC lists 6 × 7 reeving for its 3,150 and 4,500 kN rigs. [2] [3]
Sovonex and a ZJ70 limits sheet both pair 38 mm line with 1,524 mm (60 in) sheaves at 4,500 kN. [2] [4]
Sovonex builds its crown blocks to API Spec 4F and API Spec 8C. [2]
Sources checked 2026-10-11. OSHA's glossary is US government guidance; Sovonex and ZPEC are rig suppliers publishing tables for their own equipment; the ZJ70 limits sheet is an operator's document for one rig. Figures are examples.
Ask for use case, specification boundaries, supplier type, and RFQ preparation information for this product.
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