What are the vertical pieces of stock that are placed on corners for siding to butt against?

The vertical pieces of stock placed on corners for siding to butt against are known as corner boards. Corner boards serve both a functional and aesthetic purpose in siding installation. Functionally, they provide a clean, finished edge at the corners of a building, allowing siding materials to meet in a way that is secure and visually appealing. They help to create a straight line for the siding to follow, ensuring that the installation is level and properly aligned.

In addition to their functionality, corner boards enhance the overall look of the structure, providing a defined transition between different walls. They also contribute to the durability of the siding by protecting the edges from moisture and wear.

Other options, while related to building concepts, do not specifically describe the function of corner boards. Siding strips typically refer to the pieces of siding themselves, structural supports relate to the framing of the building, and framing blocks are used to reinforce structural elements but do not serve the same purpose as corner boards in siding applications.