What do extension lines represent in a blueprint?

Extension lines in a blueprint are used to indicate the dimensioning references for various components within a design. They serve as visual guides, extending from the object to the dimension lines to clarify where the measurements are taken. This is crucial for accurately conveying the sizes and locations of features in the drawing, ensuring that anyone interpreting the blueprint can understand precisely how each part relates dimensionally to others. This emphasis on dimensional accuracy plays a vital role in construction and manufacturing processes, where precise measurements are necessary for alignment and assembly.

The other options do not directly correlate with the specific function of extension lines. Shear strength is a property of materials related to their capability to withstand shear forces, and thus does not relate to representation in a blueprint. The thickness of walls is typically specified using dimension lines or notes directly on the drawings rather than extension lines. Connection points might be indicated in other ways, such as with symbols or notes that show where various elements link, not through extension lines specifically meant for dimensions.