Allen key
From Freepedia
An Allen wrench, Allen key, hex key or hex head wrench is a tool used to drive Allen screws and bolts, which have a hexagonal socket in the head.
Some of the advantages of this format of tool are:
- Six contact surfaces between bolt and driver
- Contact surfaces of the bolt are protected from external damage
- The bolt can be inserted into its socket using the key
- Torque applied constrained by the length and thickness of the key
- Very small bolt heads are accommodated
- Can be used with a headless screw
Using a single tool instead of many others reduces tooling costs for the manufacturer and is more convenient for the end user. Many manufacturers have adopted hex key bolts for assembling bicycles or for self-assembly furniture.
"Allen wrench" was originally a trademark of Allen Manufacturing Company in Hartford, Connecticut in 1943. In non-English speaking parts of Europe, it is usually known as an "Unbrako key" (also often misspelled as "Umbrako"), which is a brand name established in 1911. The brand is owned by SPS Technologies. In Germany and Netherlands, this type of screw is known under the name Inbus™, named after the company that invented them in 1936, Bauer & Schaurte Karcher in Neuss. (Innensechskantschraube Bauer und Schaurte)
Standard sizes
(American National Standard)
Machinery's Handbook 26
| Nominal | Socket Size |
| 6 | 7/64 |
| 8 | 9/64 |
| 10 | 5/32 |
| 1/4 | 3/16 |
| 5/16 | 1/4 |
| 3/8 | 5/16 |
| 7/16 | 3/8 |
| 1/2 | 3/8 |
| 5/8 | 1/2 |
| 3/4 | 5/8 |
| 7/8 | 3/4 |
| 1 | 3/4 |
Standard metric sizes: 1, 2, 3, 4, 5, 5.5, 6, 8, 10 mm.
Care should be taken by users of these tools that the measurement format of their tool matches that of the nut. While most of the world has adopted the metric sytem, the U.S. continues to use imperial units. Therefore, many goods (furniture, etc.) imported by the U.S. have metric nuts, while the unaware american may attempt to use imperial tools. This could result in damage to the nut or tool, potentially rendering the nut or tool unusable.
