Taiwan Leading Hand-Tool Maker

Socket Size Basic Knowledge

  • 2014-08-01


How to Measure Socket Drive Size

In the diagram above, the three key dimensions of a socket are labeled as Drive Hole, L, and S. These key dimensions determine the usage of this socket as follows:

Drive Hole indicates the size of the drive hole (also referred to as the "driver hole" or "square hole"), which determines the torque size of the driver tool you’ll need. For example, you’d use a ½-inch drive socket with a ½-inch drive ratchet.

L indicates the overall socket length. The length you’ll need will be determined by your working environment. For screws in deep holes, a deep socket will be your best option.

S indicates the target size of the nut, which determines which socket you’ll need. For example, you’ll require a 5mm socket for a 5mm nut.

Drive hole size

The size of the drive hole is determined by usage and torque demand. Common measurements are as follows:
1/4”(6.3mm), 3/8”(9.5mm), 1/2”(12.7mm), 3/4”(19.0mm) and 1”(25.4mm)。

Why use inch? Because this was developed in Great Britain during the Industrial Age.

Socket Drive Hole

At the hardware store, you’ll find ratchet wrenches and other spanners with the above drive-hole sizes. The bigger the drive hole, the higher the torque resistance. Smaller drive holes are suitable for confined spaces. Generally speaking, 3/8 inch (9.5 mm) is the most popular size in the auto repair industry. However, it changes country by country. 


Socket Sizes:SAE (INCH, fraction) & Metric (mm)

In the current market, socket sizes are divided into two systems: SAE (imperial, measured in inches) and metric (measured in millimeters). Both 6-point and 12-point sockets are measured using these two systems. The popular range is 5.5~24mm. SAE is used primarily in the United States and metric is used primarily in Europe and Asia.

Convert: 1 inch = 25.4mm

Socket length

Sockets are available in deep, semi-deep and standard sizes. You can select the length most suitable for your working environment. The semi-deep size is designed specifically for 3/8" DR.


As the leading manufacturer of bit sockets and impact sockets, Tien-I provides the full range of sockets and customized metal processing parts. For more information, please contact our sales team.