What Is an Allen Wrench?
An Allen Wrench is a tool used for tightening or loosening screws with hexagonal sockets, similar to a hexagon socket wrench.
These wrenches are L-shaped with a regular hexagonal tip and have different lengths for the short and long arms.
The standards for Allen Wrenches include:
- JIS B4648 Hexagonal Bar Wrench
- ISO 2936 Assembly Tools for Screws and Nuts – Hexagon Socket Screw Keys
- ASME B18.3 Socket Cap, Shoulder, and Set Screws, Hex and Spline Keys
Uses for Allen Wrenches
Allen Wrenches are typically used to fasten bolts and screws with hexagonal sockets. These specifically include:
- Hexagon socket bolts (e.g., hexagon socket button bolts, hexagon socket countersunk bolts)
- Set screws
- Hexagon socket plugs
Different types of screw heads, such as Phillips and flat, are used for various applications. Hexagonal sockets are mainly used for fastening where a higher torque is required.
Principle of Allen Wrench
The principle of an Allen Wrench is straightforward: Insert the wrench’s hexagonal tip into the hexagonal socket of a bolt or screw, and turn it to tighten or loosen. The L-shaped design, with differing arm lengths, offers versatile usage depending on the application. For areas with limited space or requiring less torque, use the longer arm for leverage. Conversely, for tighter spaces or when more torque is needed, use the shorter arm.
Types of Allen Wrenches
Allen Wrenches are classified based on size, tip shape, materials, and other features.
1. Classification by Size
Figure 1. Example of hexagonal bar wrench sizes
Allen Wrench sizes follow the JIS B4648 for millimeter sizes and ASME B18.3 for inch sizes. However, the length of wrenches sold may vary from the standard.
For JIS B4648 millimeter sizes, the bilateral width dimensions range from 0.7 to 46 mm. The length of the arms correlates with the width dimension. See Figure 1 for examples.
ASME standard wrenches come in inch sizes, with hexagonal dimensions ranging from 1/16 to 3 inches.
2. Classification by Tip Shape
Figure 2. Tip shape of hexagonal bar wrench
Allen Wrench tips come in two shapes: a standard hexagonal and a ball-point with chamfered corners. The ball-point allows for angled insertion, useful in hard-to-reach areas, whereas the standard tip is used for direct, perpendicular insertion. However, the ball-point type may not be suitable for high-torque tightening.
3. Classification by Material and Surface Treatment
Common materials for Allen Wrenches include chrome molybdenum steel, chrome vanadium steel, and stainless steel. Surface treatments like black dyeing, nickel plating, and chrome plating are common, except for stainless steel wrenches.
4. Others
Figure 3. Hexagonal bar wrenches with holder and folding type
Allen Wrenches also come in sets with holders or as folding types, where multiple sizes are contained in one tool. This design is convenient for storage and selection of the required size.