Posted by Clint Dixon [172.68.90.19] on Thursday, February 21, 2019 at 10:17:30 :
In Reply to: Re: Easier to read posted by Andrew in MI [172.68.206.115] on Wednesday, February 20, 2019 at 22:15:08 :
With cut threads, the material starts out at approximately the same size diameter as the intended major thread diameter. Sometimes larger, rarely smaller. In the case of my U-bolts, the overall diameter of the forged legs measure between .560 and .566 diameter. The threads are then cut into the cylindrical shapes resulting with material being removed and discarded.
With rolled threads, the material starts out at a much smaller diameter than the intended major thread diameter. In the case of my NOS overload kit U-bolts (which are not forged),.525 diameter. The threads are then rolled (formed) with material being displaced from the root of the thread (minor diameter) and being packed into the crest (major diameter) with none ever being discarded. The diameter of the material actually grows.
With cut threads, you can extend them by running the cutting die further down the length of material. With rolled threads, if you try to extend them with a cutting die, the resulting threads will have very short flat crests and will be weak because you are trying to cut into material that is too small of a diameter.
A good example for comparison would be to lay side-by-side an original head bolt (rolled threads) and a common grade 2 bolt from a hardware store (cut threads). The difference is clearly visible.
Junior