Single point thread tools

[magicniner]

Larger diameters for a given pitch, have a less angled thread, so to ensure a 100% correct thread form, the cutter has to be angled to compensate for the thread angle, however if you need that level of accuracy in your threads, you probably won't even be considering thread milling.

If you need a full thread right to the bottom of a flat bottomed blind hole you probably won't even be considering anything other than thread milling.
If you need a thread with specific start/finish points for alignment of two mating parts you probably won't even be considering anything other than thread milling.
If you want one tool in your drawer that will get you a working part covering a huge range of threads you probably won't even be considering anything other than thread milling.

Job specific threadmills can produce perfectly accurate thread forms and full forms too, not partial, what you have to understand is that the form of the tooth on the tool differs not just for different thread angles but also for different diameters of tool, outside threads versus inside threads and different ranges of Major Diameter, knowing these the manufacturer designs a cutter profile which when swept through the work and following a helical path generates the correct thread form.
Single point inserted thread milling tools are a great thing to have around, they are specifically produced because they allow a wider range of threads to be cut, albeit with reduced accuracy, but in this situation it is clearly incumbent on the programmer/operator to ensure the resulting thread is close enough to spec to be acceptable.
If you need a higher level of accuracy in your threads you probably won't even be considering not buying the correct threadmill for the job. ;-)

- Nick