Excellent for dimensioning bolts, screws, nuts (USS, SAE and Metric) and twist drills to measure. You measure the bolt diameter by sliding the bolt through the dimensioning holes. Also measures hex nuts and washers. The back of the gauge includes a feature to measure U.S. and metric thread pitches. Special notches on the front of the tool allow you to measure flat headed metal and wood screws. Made from sturdy, lightweight green plastic that resists water, alcohol, oil and grease.