Hello, which type of coupling (e.g. plum shaped, bore rigid, flexible, etc.) is best to connect a 8mm D-shaped shaft (shaft length 20mm, D-cut length 15mm) from a NEMA stepper motor to an end of a 16mm SFU1605 ballscrew (seems to have 10mm diameter at the ends)? Can't seem to find one with a set screw to fixate the D shaft.