I find that those set screw couplers that come with printer kits often fall short of providing an accurate and smooth motion because it's very difficult (sometimes impossible) to center the shaft and the lead screw in the coupler. This can lead to wobbly lead screws and z-banding. I designed this to use M3 Nuts and Bolts to clamp around the D-Shaft of the stepper and a T8 lead screw, which provides an adequate friction fit and perfectly aligns the two. There is ZERO flex between the two, and this may cause issues on cheaper machines that needed that "give" that the old coupler allowed for.
Side note, the M3 Nut recesses may be snug since this is printed vertically (which I recommend). I suggest putting the nut on the first few threads of a bolt and then using the bolt to shove the nut into place, then simply twisting the bolt counterclockwise to release it and leave the nut in there.
In total, you'll need
8x M3 Nuts
8x M3 Bolts (at least 6mm in length)