Using thread mills give you better flexibility to produce the thread you need and control it. The same tool can make different range of hole sizes. It gives you better flexibility on producing internal, external, left and right threads. Not like screw taps, that can break inside the hole and damage the whole product, thread mills do not have this danger and usually has longer life time.
Usually the customer knows his application, machine and preferences. However, Helical flutes have few advantages, the main advantage is the progressive contact with the material, especially when the material is hard. It prevents high pressure on the tool and extend its working life.
A straight tool is usually less expensive and enable renewing it. (therefore reducing the tool’s diameter)
Carbide Grade : M5C-Submicron PVD coated (TiANL) For general purpose.