This product is used to upgrade the Z-axis screw of Ender3 S1/S1 pro 3D printer. Compared with the original T-screw, the ball screw can bring higher precision, printing speed, load, smoothness, service life, etc. Compared with T-screw, the ball screw has different friction mode, rolling friction has less resistance and more stable running track. In addition to the advantages in principle, Whether it is material or processing accuracy, ball screw requirements are much higher than T screw. Considering weight, size and accuracy, this kit is SFU1204 with 12mm thread diameter and 4mm stroke.If you have any installation questions, please feel free to contact us, we will reply you within 24 hours. At the same time, you are welcome to enlighten any defects or suggestions related to the product. Your opinions are our driving force for continuous improvement. Our belief is that we are willing to make 100 percent efforts for one percent progress.