The 3541 fracture mechanics clip-on gages are compliant with standardized test methods, including ASTM E1820 for the determination of properties with fracture toughness in metallic materials. They also conform to requirements for JIC and R-curve determination. For various fracture mechanic tests, clip-on gages are used. These types of tests include arc shaped, compact tension, bend specimens, disc shaped, etc. Also, the clip-on gages can be used directly on the specimens, particularly those in which knife edges are crucial. Bolt-on knife edges are optional, and can be mounted on the specimen. Special models that meet ASTM E-399 accuracy requirements are available. The gages are fully enclosed for protection from accidental damage. The case is designed with quality foam lining. All models have high frequency capabilities for operation.