- Apr 14, 2014
H2 likely is the type of HSS the tool is made of; this is a common marking for tools of this sort.
This was more important for precision gears when all components of the machine were mechanical. The hob had to fit precisely to insure proper depth and clearance. Now that most machines have hydraulically controlled spindles they can keep uniform and constant pressure against the work piece so an .0005" difference in fit to the spindle can be compensated for.