Jim,
Standard threads you see on a bolt, the Thread is a single start. If you look at the end of a 1/4-20 x 1" you will see one thread end (or blend) off the end of the screw / bolt. That is one constant thread that twists 20 times in the inch. Thus a single "Start"!
In the case of an "Acme" thread you will see the end is totally different. If you have a piece of Acme, machine it with a flat on the end, it will have more than one thread that "Ends" on that flat, Thus 2-4 + Start's. Its the geometry that makes it different than standard thread.
Yes, the more "Starts" on the thread, the more engagement you get on the nut thus the more or tighter tollerances. But again, the more starts, the Less Turns per inch you get. It is a give and take.
Hope I answered your question, assuming your not pulling my leg!
Glen |