6 mm OD Micro Reli-A-Flex Coupling. This is a flexible beam type coupling that is secured to the shaft via set screws.
Product catalog can be found here.
Product page can be found here.
These couplings are used to connect two shafts together in order to transmit motion. These differ from power transmission couplings because they are designed for motion control applications where very smooth motion and torsional stiffness is required. Many hours of testing and analysis have produced a design that provides the best balance between low bearing load, zero backlash, and torsional stiffness. This product handles axial offset, angular, and parallel better than most competing products. We have the world's smallest standard production coupling in our product range.