Crane and rigging terms glossary for NCCCO
The NCCCO written exams grade exact meanings. A candidate who knows the difference between gross and net capacity, or between radius and boom length, picks up points that a candidate with the same experience but fuzzier words loses. This glossary groups twenty terms by what they help you decide, gives each a one-line meaning, and links a full page with an original drawing, a worked example on our invented charts and the mix-ups that cost points.
Every explanation here is in our own words. Capacity figures come only from Boom Angle's invented practice charts, never from a manufacturer's chart or a code book. Where a rule matters, we cite the OSHA section number and send you to the rule itself.
Capacity and the load chart
What the chart prints, what comes off it and why the number is what it is.
| Term | In one line | Full page |
|---|---|---|
| Gross vs net capacity | The chart's printed number, and what is left for the load after deductions | Gross vs net capacity |
| Capacity deductions | Block, rigging, jib and attachments: everything the boom carries besides the load | Crane capacity deductions |
| Structural vs stability limits | Strength of the parts versus the load that would tip the crane | Structural vs stability limits |
| Load moment | Weight times distance from the pivot, and why more radius is harder | Load moment |
| Rated capacity indicator vs limiter | A device that warns versus one that also stops the motion | Rated capacity indicator vs limiter |
Try one question
Question 1 of the free 10-question check on NCCCO written. No signup.
Operations
Which action creates side loading on a crane boom?
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Geometry and working areas
Where the load is, and which part of the chart applies to it.
| Term | In one line | Full page |
|---|---|---|
| Radius vs boom length | Horizontal distance to the load line versus length along the boom | Crane radius vs boom length |
| Boom angle | The boom's tilt above horizontal, and how it sets radius | Boom angle |
| Boom deflection and loaded radius | Bending under load moves the tip out, so the loaded radius is longer | Boom deflection and loaded radius |
| Quadrant of operation | The working area a set of ratings applies to | Quadrant of operation |
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Stability and setup
What holds the crane up, and what it sits on.
| Term | In one line | Full page |
|---|---|---|
| Tipping axis | The line on the ground a crane would pivot about | Tipping axis |
| Outrigger setup | Beam extension, jacks, floats and mats matched to the chart | Outrigger setup |
| Outrigger mats and ground pressure | Force divided by bearing area, and what a mat does to it | Outrigger mats and ground pressure |
| Tail swing | The rear of the upper works sweeping wider than the carrier | Tail swing |
Operating hazards
Forces and contacts that the chart does not rate.
| Term | In one line | Full page |
|---|---|---|
| Two-blocking | The hook block meeting the boom tip sheaves | Two-blocking |
| Side loading | A pull across the boom instead of along it | Side loading |
| Shock loading | The extra force of a sudden start, stop or jerk | Shock loading |
Rigging
What connects the load to the hook, and the limits on each piece.
| Term | In one line | Full page |
|---|---|---|
| Sling angle factor | How much extra tension a flatter sling leg carries | Sling angle factor |
| Center of gravity of a load | The point the hook must sit over, and how it splits load between lift points | Center of gravity of a load |
| Choker vs basket hitch | How each hitch carries load and changes a sling's rating | Choker vs basket hitch |
| Rated capacity vs working load limit | The crane's limit versus the limit on each piece of gear | Rated capacity vs working load limit |
How these terms show up on the written exams
Under the 01/25 candidate handbook, the Core exam has four domains: Site (about 22%), Operations (about 28%), Technical Knowledge (about 23%) and Load Charts (about 27%). The terms above spread across all four. Ground, mats and tail swing are Site topics. Aids, dynamic and side loading, and deflection sit in Operations. Rigging and stability physics belong to Technical Knowledge. Radius, work areas, deductions and net capacity are Load Charts.
The Core exam allows no calculator, so the arithmetic in these pages is meant to be done by hand. Specialty exams allow a calculator and put more weight on load charts. If you are choosing between exams, the specialty written exams comparison lays them side by side.
Practice with the tools
- Load chart practice: practice problems on invented charts, from lookup to net capacity.
- Net capacity worksheet: gross, deductions and net, step by step.
- Crane radius and boom angle calculator: radius, angle and boom length from any two.
- Sling angle calculator: leg tension and angle factor for a two-leg sling.
- Outrigger pad calculator: pad size from a float load and an allowable ground pressure.
For how a chart is read from start to finish, see how to read a crane load chart, and for the exam itself, the Core written exam guide.
Know the words? Take the free 10-question check
Take the free 10-question check. It is scored by the Core outline domains and needs no signup, so you see whether site, operations, technical knowledge or load charts costs you the most points. Boom Angle's course then gives you a question bank with each answer key checked by a second solve, timed practice exams, and a study plan built from your exam date.
Sources
Show the list
- Mobile Crane Operator Candidate Handbook, CCO, Core outline domains and weights (01/25 revision).
- 29 CFR 1926 Subpart CC: Cranes and Derricks in Construction, OSHA.
- Boom Angle practice charts, original invented data. Every capacity figure on the term pages comes from them.
Facts checked 25 October 2026 against the sources listed above. If something has changed, tell us and we will correct it within 2 business days.
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