In the context of single-frame scaffolding, the piece that connects the ledger to the structure itself is known as a "putlog." Let's explore this further to understand why this is the correct option and how it differs from other components in scaffolding:

1. Definition and Role of a Putlog:
   • A putlog is a horizontal member in scaffolding which connects the ledger to the wall of a building. It is usually a short, easily adjustable piece that helps to stabilize the scaffolding structure.
   • The end of the putlog is typically flattened or shaped to rest on the wall or building structure, providing a point of support.
2. Other Options Explained:
   • Toe Board: A toe board is a safety barrier placed at the edges of scaffold platforms to prevent tools or materials from falling.
   • Guardrail: A guardrail is a protective rail mounted along the edge of scaffolds, platforms, and walkways to prevent falls.
   • Brace: A brace in scaffolding is a diagonal or horizontal support that adds stability to the structure, helping to prevent collapse or sway.
3. Justification of Correct Option:
   • The question specifies that the component in question connects the ledger to the structure. A putlog fits this description as it is designed for this purpose, establishing direct support from the scaffold frame to the building itself.

In conclusion, the correct answer is Putlog because it serves the specific function of connecting the scaffold ledger directly to the structure, providing essential support and maintaining stability.