Good engine performance requires the proper spark plug gap. You can measure and set the gap in minutes to fit the specifications of your engine.
Find the “gapping wire” that matches the recommended gap. Then slide it between the center and side electrodes. When the gap is correct, the gauge should drag slightly going in and out. If the gap is too large or the wire won't fit, adjust the side electrode.
Hook the side electrode with the gauge's bending arm. Then pivot the arm in or out in small increments to open or close the gap. Recheck with the gauge until you get a snug fit.
Spark plugs don't come gapped for your particular engine. For the best performance, you must gap the plug to the engine manufacturer's specs. If you're buying a plug for a small engine, ask the parts store to look up the gap size info for you. If the plugs are for your vehicle, find the info in the owner's manual. Then adjust the gap as shown.