The end of the spring material is beveled before it is rolled into shape. It is a very nice tight fit, most of the guys are good at what they do. I have never watched the actual heating and bending process, so not sure what type of equipment they use. But, I have always been happy with the results and the price. The last 33 Ford front main spring I had made took less than 24 hrs and cost $25.
Just looked up and watched a video of how the eyes are rolled. It is a fairly quick procedure, interesting.
https://www.bing.com/videos/search?q...8&&FORM=VRDGAR
The eye forming parts is between 1:50 and 2:10.