INSPECTION OF CONVEX AND CONCAVE SURFACES: This radius gauge set includes two types of chopped sheets to allow inspection of convex and concave surfaces. Radius gauges measurement range is R1-6.5/R7-14.5/R15-25. USES FOR: These radius gauges used to compare the measured arc to determine the radius of the measured arc. The convex pattern is used to detect concave surface arc, and the concave pattern is used to detect convex surface arc. WIDELY APPLICABLE: The radius gauge is a very useful gauge for tool makers, mold makers, mechanics and many other workers to check the radius of tools. 3 DIFFERENT SHAPES AND SIZES OF GAUGES: Radius gauge set contains four different shapes and sizes of radium gauges to meet your different needs. HIGH QUALITY MATERIALS: The rayon gauge set is made of stainless steel, durable and anti-rust, long lasting. Color: Silver Shipping Quantity: 3 pieces Due to the light and screen difference, the item's color may be slightly different from the pictures.