Nut and Bolt Thread Checker: Bolt Size and Thread Gauge The bolt size and thread gauge is an accurate, easy-to-read, and durable identification gauge that quickly measures bolt length and nut diameter, easily separating metric from rigid thread sizes, saving you time and increasing your efficiency. Bolt and Nut Identification Gauge: The nut and bolt thread checker recognizes nuts and bolts in 28 sizes, 14 inches and 14 metric. Each size has an external thread for nuts and washers and an internal thread for bolts and screws, which makes it easy to distinguish between different nuts and bolts. Durable: The nut and bolt thread checker is machined with carbon steel. The bolt size and thread gauge can be installed in your toolbox or wall. We have provided reserved holes for hanging. No need to drill anymore. Two sizes: The nut and bolt gauge is available in inches and centimeters along the edge to help you quickly identify different thread sizes. Color: Black Material: Carbon steel Package