The screw itself uses a special spherical thread. That is, it is not made with a pointed angular cutter, but it appears to be made by rolling. The surface is very smooth as you can easily see in the photo.
Special thanks to Mr. YM Wong for lending me this example of the ball screw.
The smaller object represents the "nut" through which the lead screw would normally pass. It contains ball bearing arranged to the pitch of the screw.

The larger round object is a high-quality ball thrust bearing.
Here is a close-up view of the thrust bearing

Here is a close-up view of the ball bearing nut and the thrust bearing.
Back to my home page
You can see the geometry of the main screw thread. Not the smooth round shape of the thread. The little grooves also have something to do with the ball bearing nut, but I'm not quite sure what its exact function is!

Another close-up view of that gorgeous thread geometry.

Only very expensive machinery will utilize this type of screw. If only our 7x10 ran on these!!!!!