The number of screw threads per inch for a Standard National Coarse 1/2 inch bolt is __________.

Correct Answer: Option A — 13

Under the Unified Thread Standard, a 1/2-inch National Coarse (UNC) bolt is specified as having 13 threads per inch. This standard thread pitch is essential for ensuring compatibility between fasteners and tapped holes, maintaining the structural integrity of machinery assemblies as required by marine engineering standards.