An extensional fixture is a specialized testing apparatus used to apply tensile forces to a sample in order to measure its response to extensional or elongational deformation. The fixture typically consists of two clamps or grips that securely hold the sample in place, with one clamp fixed and the other movable. When the movable clamp is pulled away from the fixed clamp, the sample is subjected to tensile stress, causing it to elongate and deform. This deformation can then be measured and analyzed to determine various material properties, such as extensional viscosity, elongation at break, and tensile strength. Extensional fixtures are commonly used in materials science and engineering to characterize the mechanical behavior of polymers, elastomers, and other materials under extensional stress.