What is the purpose of the collar on a hi-shear rivet?

The purpose of the collar on a hi-shear rivet is to act in place of a bucktail. In a traditional blind rivet or a solid rivet, the bucktail is the part of the rivet that expands to create a mechanical lock upon installation. Hi-shear rivets are specifically designed for high-strength applications and the collar functions similarly to a bucktail by providing anchorage in the structure being riveted.

By replacing the bucktail design, the collar allows for easier installation and ensures that the rivet can withstand shear forces, making it suitable for critical applications, such as in aviation structures where strength and reliability are paramount. This feature creates a secure and robust connection in the panels being fastened, ensuring structural integrity under operational stress.