Which command is best used to strengthen joining surfaces in a model?

The use of the fillet command is ideal for strengthening joining surfaces in a model because it creates a smooth, rounded transition between two surfaces or edges. This rounded geometry helps to eliminate sharp corners, which can be stress concentration points that lead to failure under load. By adding a fillet, you not only improve the aesthetics of the design but also enhance its mechanical integrity.

Fillets distribute stress more evenly along the joining surfaces, making them more robust during operation. This is particularly critical in applications where the parts will experience bending, torsion, or other forces. The filleting process effectively increases the surface area of the joint, allowing for better load distribution and reducing the likelihood of crack initiation.

Other commands, while useful in their contexts, do not serve the same purpose as the fillet. For example, a chamfer creates a beveled edge, which can also help in certain design scenarios, but it does not offer the same level of stress reduction as a fillet would. Patterns and offsets serve different functions related to duplication of features and modifying sketch shapes, respectively, rather than reinforcing structural connections. Therefore, the fillet command is the most effective for strengthening joining surfaces in a model.