Which tool is typically not used for fastening materials securely while they are worked on?

Choosing aspiration clamp as the answer reflects an understanding of the tools commonly employed in pipe fitting and other types of construction work. The primary function of an aspiration clamp is not to fasten materials securely during work; instead, it is often used to hold or grip objects lightly without the firm locking mechanisms that tools like a bench vise or vice provide.

In contrast, both the bench vise and vice are designed specifically for securely holding workpieces, allowing for stable handling during cutting, drilling, or assembling tasks. These tools feature robust clamping abilities that ensure materials do not move during the application of force or tools.

A strap wrench, while primarily used to grip round objects and prevent slipping, can also facilitate the steady handling of materials. However, its typical usage context differs from that of the more stationary and robust clamping capabilities of a bench vise or vice. In essence, the aspiration clamp's purpose and design differentiate it from these fastening tools, making it the correct choice for the question.