Applications - Works with most spark plugs that have gap sizes of 0.394 in, 0.472 in, 0.551 in, and 0.630 in. Not compatible with plugs with a thread diameter of 0.709 in or larger. Warning - Some spark plug electrodes may rebound after adjustment. If your target gap is 0.015 in and the recommended value is 0.015 in, the backlash can be up to 0.015 in. Reliable performance - This universal spark plug gap tool enables precise adjustment of the spark plug gap. To use, attach the spark plug to the gap tool and slowly turn the knob to set the gap. Premium quality material - Made from high-quality aluminum alloy, it offers high hardness, is not easily damaged, and is sturdy and durable. Use scenarios - Automotive maintenance: perform routine plug replacement and gap verification for gaps within 0.394–0.630 in. - Motorcycle and small-engine service: convenient for bikes and small engines using the listed gap sizes. - Field diagnostics: quick, repeatable gap setting in shop or on-site service.