A spark plug gap is the distance between the end of the electrode and the base of the spark plug. If your spark plugs aren’t properly gapped, your engine may not burn fuel properly. Since every make and model requires a different gap size, start by looking in the owner’s manual for your vehicle to find the required gap size, or pull the information up online. Then, grab a gauge tool, and slide the recessed lip under the electrode sticking out from the base of the spark plug. Rotate the disc until you feel a firm resistance and check the measurement next to the lip. If the gap matches your required size, you’re good to install it in your vehicle. If the gap is too small, pull the body of the plug away from the disc with the electrode hanging on the lip to gently force the gap open and re-measure it. If the gap is too big, use the broad side of the gap tool to push the electrode down and make the gap smaller. Continue re-measuring and making minor adjustments until the gap in the spark plug matches your manufacturer’s recommended gap size. For tips on choosing an appropriate gap tool, read on! more