INSPECTION OF CONVEX AND CONCAVE SURFACES: This radius gauge set includes two types of thin sheets to allow inspection of convex and concave surfaces. The measurement range of radius gauges is R0.3-1.5/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 the arc of concave surface, and the concave pattern is used to detect the arc of convex surface. 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. 4 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 radius gauge set is made of stainless steel, durable and rustproof, long lasting.