I needed an 8-32 x 0.760" long stainless steel machine screw recently. A 1" long one would not work, and I could not find a 7/8" long one anywhere that I tried. (And I'm not sure that 7/8" would have worked, anyway.) So how to cut down such a small screw? You can't really hold safely under a chop saw, or a band saw and even if you could, you would need to run it through a die to get the threads at the end clean. I discovered that my lathe chuck would not hold it solidly enough centered--it is just too small.
What I did was to drill and tap an 8-32 hole through a piece of acetal so that the screw would stick up through the top of the acetal block. Now I could clamp the block down solidly in the vertical mill, and take repeated .010" passed across the top of a 1" long 8-32 screw until I had reduced it to the correct size. Best of all, the process was so precise that I did not need to clean up the threads.