A flexible coupler with a 6.35 mm (1/4 inch) bore on one side and 8 mm on the other side, ideal for connecting a NEMA23 motor (or one of the rare NEMA17 motors with 6.35 mm shafts) to an M8 threaded rod, for example for the Z axis of an eShapeOko CNC milling machine.
Usually, flexible couplers have either a set screw, or a slit that forms two jaws that can be tightened with a screw. This coupler has both, which is an advantage. Using both mechanisms to tighten it helps keep it centered, especially when the object it tightens around is slightly smaller than the nominal diameter (M8 thread, for instance, is hardly ever fully 8 mm in diameter).
Overall dimensions: length 25 mm, diameter 20 mm (jaw tightening screws protrude slightly).
Material: aluminium alloy, steel.
Part number: EM-FC6-8 (replaces EM-FC5-8 in the eShapeOko, or SM-H12 in the ShapeOko, both of which are 5 mm to 8 mm couplers).