DOR HSCO TAP M18NO8

Bottoming chamfers have 1 to 2 threads. Plug chamfers have 3 to 5 threads. Taper chamfers have 7 to 10 threads and are typically used as a starter tap. They all can be used for threading blind holes
Oxide, also known as black oxide or steam oxide, is a surface treatment that prevents chip building, galling and welding on the workpiece. It is commonly used on low carbons, stainless steel and ferrous metals

Cobalt is harder than high speed steel and provides better wear resistance. It is commonly used on high tensile alloys