A standard fillet weld has a right-triangle cross-section with equal legs. What are the base angles of this triangular section?

Introduction / Context:Fillet welds join two members at right angles or on a lap. The standard fillet section is a right triangle with equal legs, and its geometry governs throat thickness and design strength.

Given Data / Assumptions:

• Standard, equal-leg fillet weld.

Concept / Approach:In an equal-leg right triangle, base angles are equal and sum with the right angle to 180°. Hence each acute angle is 45°.

Step-by-Step Solution:Right angle = 90°.Sum of angles = 180° ⇒ remaining 90° shared equally.Each base angle = 45°.

Verification / Alternative check:Welding handbooks define standard fillet geometry with 45° legs, from which throat thickness = 0.707 * leg follows.

Why Other Options Are Wrong:

• 30°–60°, 40°–50°, 20°–70°: not equal-leg fillet geometry.

Common Pitfalls:Confusing leg angle with included angle between members; using unequal-leg fillet data.

Final Answer:45° and 45°