iPhone or iPad
- Open Crazy Nuts in Safari.
- Tap the Share button.
- Select Add to Home Screen.
- Confirm by tapping Add.
How to use and understand Crazy Nuts
Crazy Nuts compares the actual opening of spanners, sockets and hex keys. It also shows the closest commonly available alternative when an exact equivalent is unavailable.
- Choose the tool type.
Select Spanner / socket for an external bolt head or nut. Select Hex key for an internal hexagonal recess.
- Choose the sizing system.
Select Metric, AF, SAE, BS / BSF or Whitworth. Hex keys use Metric, AF and SAE because BSF and Whitworth are thread-based external-tool markings.
- Choose the marked size.
Select the size printed on the tool or the size you already know.
- Read the actual measurement.
The teal result area converts the selected size into its physical width in millimetres.
- Compare the equivalents.
Each result card shows the nearest included size in the other systems, its actual opening and the difference from your selection.
- Check the recommendation.
The practical-fit section lists sensible tools that should physically engage the fastener. Always prefer an exact fit when significant force is required.
| Exact match | The nominal dimensions are the same. |
|---|---|
| Close fit | A small difference exists. Inspect the tool and fastener and use moderate force. |
| Caution | The substitute is noticeably loose and may round the fastener under load. |
| Too small / large | The tool is not expected to fit correctly in the selected application. |
| Poor fit | The difference is too large for the tool to be recommended. |
Workshop safety: The guide compares nominal dimensions. Coatings, manufacturing tolerances, damaged corners and wear can change the real fit. Use a six-point socket or ring spanner where practical, and measure the fastener when uncertain.
Install Crazy Nuts for out-of-service use
Open Crazy Nuts while connected to the internet before relying on it offline. Installing it adds an app-style shortcut and keeps the converter and Help page available when mobile reception or internet service is unavailable.
Android
- Open Crazy Nuts in Chrome.
- Open the browser menu.
- Select Install app or Add to Home screen.
- Confirm the installation.
Computer
- Open Crazy Nuts in Chrome or Edge.
- Select the install icon in the address bar, or open the browser menu.
- Select Install Crazy Nuts.
- Confirm the installation.
Before heading out: Open the installed app once while online. Reconnect and reopen it occasionally to receive updated sizes, guidance and fixes. Conversion features work offline. Advertising and optional analytics are not loaded in installed standalone mode.
Where each system is used
The same fraction can mean different things depending on the system. Metric, AF and SAE tool markings normally state the opening directly. Classic BSF and Whitworth markings normally identify the thread diameter instead.
Metric
A 10 mm tool is nominally 10 mm across its working flats.
Commonly found in: modern automotive work, motorcycles, bicycles, machinery, manufacturing, construction, appliances and general maintenance throughout Australia and most of the world.
AF - Across Flats
AF describes the physical distance between two opposite parallel flats. A 3/8 AF tool is exactly 3/8 inch, or 9.525 mm, across the opening.
Commonly found in: older British and American vehicles, imported machinery, aviation, industrial equipment, restoration and mixed imperial tool sets. AF is a measurement description, not a thread family.
SAE
SAE tool sets commonly use fractional-inch openings. A 3/8 SAE socket has the same nominal opening as a 3/8 AF socket.
Commonly found in: North American vehicles, engines, machinery, workshop equipment and imperial fasteners used in automotive, agricultural and industrial work.
BS / BSF
British Standard Fine uses a fine-pitch thread. The marked spanner size normally refers to the bolt's nominal thread diameter, not the distance across the head.
Commonly found in: vintage British vehicles and motorcycles, older machinery, agricultural equipment, military equipment, heritage engineering and restoration work.
Whitworth
British Standard Whitworth is an older coarse-thread system. Its classic spanners are marked with the nominal thread diameter rather than their physical jaw opening.
Commonly found in: early British vehicles, steam equipment, locomotives, machine tools, farm machinery, marine equipment and heritage restoration.
Advertising and donations
Crazy Nuts is free to use and is supported by advertising. Advertising does not influence the conversion values or tool recommendations.
Optional donations are gratefully accepted and help fund further development, testing, hosting and additional workshop tools.
PayPal offers AUD $5, $20 and $50 choices plus a custom amount. Cryptocurrency supporters can choose from the addresses listed by Jays n Dees. Where the selected network supports a transaction note, please include Crazy Nuts.
Internet connection required: Payment services and cryptocurrency addresses are not stored inside the offline WebApp.
Contact Jays n Dees
Found an incorrect size, need help, have a feature suggestion or would like to support further development?
Visit the Jays n Dees Contact page and include Crazy Nuts in your message so we can identify the WebApp quickly.
Contact Jays n Dees