What is the name of the wood member that is graded by its bending strength, measuring 2-4 inches thick and at least 6 inches wide?

The correct answer is joists because joists are structural members that support horizontal loads and are specifically graded for their bending strength. Typically, joists are made of dimensional lumber and are designed to span across open spaces, providing support for floors or ceilings. They are usually sized to be 2-4 inches thick and a minimum of 6 inches wide, which aligns with the specifications given in the question.

Understanding the significance of grading by bending strength is crucial for ensuring that the structure can adequately support the intended loads. Joists are central to the integrity of many building designs, which can include residential and commercial structures. The grading helps to specify which materials can safely be used in particular applications based on their load-bearing capacity.

The other options do not fit the description as accurately. Timbers refer to larger members used for heavy construction but may vary in dimensions beyond the specified range. Sills are typically horizontal members at the bottom of a wall, serving as a base rather than a load-bearing structural element in the way that joists do. Studs are vertical members used in wall construction and are usually narrower than 6 inches wide, thus not meeting the criteria outlined in the question.