**Shank Length of a Bolt**

The shank length of a bolt refers to the portion of the bolt that extends from the threaded portion to the head of the bolt. It plays a crucial role in the structural integrity and performance of the bolted joint.

**Importance of Shank Length**

The shank length of a bolt is important because it determines the amount of grip length available for the joint. The grip length is the portion of the bolt that engages with the material being fastened. It is essential for ensuring that the joint remains secure and resistant to loosening or failure.

**Factors to Consider**

When determining the appropriate shank length for a bolt, several factors should be taken into account:

1. **Bolt Diameter**: The diameter of the bolt is an important consideration. It determines the load-carrying capacity of the bolt and affects the strength and stability of the joint.

2. **Material Thickness**: The thickness of the material being fastened is also a crucial factor. The shank length should be sufficient to ensure that the bolt engages with an adequate amount of material to provide a secure and reliable connection.

3. **Thread Engagement**: The threaded portion of the bolt should be long enough to provide sufficient thread engagement with the nut or the tapped hole. This ensures proper load distribution and prevents stripping or shearing of the threads.

4. **Clearance Requirements**: Depending on the application, there may be clearance requirements that dictate the maximum shank length. For example, if the bolt is being used in a confined space or in close proximity to other components, the shank length may need to be limited to prevent interference.

**Recommended Shank Length**

Generally, the shank length of a bolt should not be greater than a certain multiple of the bolt diameter. The appropriate multiple depends on the specific application and design requirements. It is important to note that these recommendations are not universal and may vary depending on the applicable design codes and standards.

In the given options, the most suitable answer would be **(2) 4 times the bolt diameter**. This recommendation is based on industry standards and best practices for bolted joint design. A shank length that is four times the bolt diameter provides a good balance between grip length, thread engagement, and overall joint integrity.

Exceeding this limit may result in inadequate thread engagement, reduced clamping force, and increased risk of joint failure. Similarly, a shank length that is significantly less than four times the bolt diameter may not provide sufficient grip length, compromising the strength and stability of the joint.

It is important to consult the applicable design codes, standards, and engineering principles to determine the specific shank length requirements for a given application.