Finger Gauge - Metal Flat Wide - Sizes US 1-15 - SFC Tools - 35-0187 Flat wide metal finger gauges measures the size of fingers in American sizes. Each of the 29 finger gauges is marked with its size. Sizes range from US size 1 (12.37mm) to US size 15 (23.9mm) and come on a steel ring. Each gauge is 6 mm wide and very sturdy.