Feeler gauge sets have multiple thin strips of metal or plastic housed in a lockable holder. Also known as thickness gauges or gap gauges, they are inserted individually or in combination between two objects to measure the distance or gap between them. These sets have gauges of varying shapes and sizes that are marked with the thickness and often the standard/metric equivalent and/or thickness tolerance so it’s easy to see the thickness without needing a separate gauge to keep them straight. They are commonly used in engineering, machining, woodworking, or automotive applications.