The Sandia Mechanics Challenge (SMC) provides the solid-mechanics community a forum for assessing its ability to predict mechanical behavior in structures and materials through a blind, round-robin format. Computationalists are asked to predict the behavior of an unfamiliar geometry given experimental calibration data, their predictions are compared to experimental measurements of the SMC scenario, and then the participants assess and compare their approaches, documenting their findings. The SMC broadens the scope of Sandia-hosted benchmarking problems that previously focused on ductile failure through the Sandia Fracture Challenges, enabling an enduring, community-wide self-assessment of predictive capabilities for a variety of mechanics topics. The SMC is part of the Structural Reliability Partnership, which offers other benchmarking challenges hosted by several participating institutions. The topic of the SMC2023 is threaded fastener joints, specifically the deformation and failure of a structure with a threaded fastener joint in a drop scenario. Much of the research on predicting threaded fastener joint behavior has been on joints in vibrational environments or loss of joint preload. Less attention has been paid to the large deformation and failure of threaded fastener joints, even though analyses of such scenarios are vital to safety assessments of structures with threaded fastener joints. These analyses require modeling of several phenomena including multi-axial joint mechanics, material deformation and failure at intermediate strain rates, and contact mechanics. This SMC is calling attention to these diverse and challenging analyses, rallying the solid-mechanics community to identify and address potential shortcomings. This information packet enables participants to perform their predictions. The SMC scenario is a drop of a metal structure with a cantilevered cylinder attached to a block by threaded fasteners. The information packet includes a description of the SMC scenario and geometry, calibration data for the metal materials and fasteners, and quantities of interest from the predictions that serve as the basis for comparison to the experimental data of the SMC scenario. Participants will be asked to perform their predictions in a limited amount of time, on the order of a few months, to mimic real-world time constraints of safety assessments. After the predictions are returned, the SMC organizers will conduct the initial comparisons of the predictions and experiments, and then all participants will work together to assess the predictive capabilities and report the results. The SMC will enable the solid-mechanics community to define the state-of-the-art in modeling the behavior and failure of structures with threaded fastener joints, highlighting where future research could improve the approaches.