You are ordering a new block to use with a 3-inch circumference manila line. Which represents a proper size block for this line?

Correct Answer: Option B — 9-inch cheek, 6-inch sheave

The rule of thumb for block sizing is that the block shell length in inches should be approximately three times the circumference of the manila line. For a 3-inch line, a 9-inch block is appropriate. A 6-inch sheave provides the necessary diameter to minimize rope fatigue.