A shaft coupler is a mechanical device used to connect two shafts with different diameters. This coupler is designed to fit shafts with a diameter of 4mm on one end and 8mm on the other, allowing for a secure and stable connection. The coupler has a helical cut that allows two shafts that are not perfectly aligned to be joined together while reducing binding. The helical cut means these are a little springy in the X, Y, and Z axis but not in the rotational axis meaning they will not cause additional backlash.