The dimensions of a nominal 6" x 8" x 16" concrete masonry unit are what?

The correct answer is based on the standard dimensions of a nominal concrete masonry unit, specifically the nominal size of a 6" x 8" x 16" block. The nominal size refers to the intended measurement, which includes allowances for mortar joints. In practice, concrete masonry units are typically smaller than their nominal size to accommodate these mortar joints when they are installed.

For a nominal 6" x 8" x 16" block, the actual dimensions are 5 5/8" x 7 5/8" x 15 5/8". This is because the nominal dimensions account for an additional 1/2 inch in each dimension that is lost to the mortar. The standard adjustment is to subtract 3/8 inch from each of the nominal dimensions (for the mortar joint thickness and the way blocks are manufactured), resulting in the dimensions stated above.

Thus, option A provides the correct actual dimensions, directly reflecting the industry standards for concrete masonry units, making it the accurate choice.