They are made of high grade steel rounds (grades 12 to 15).

Dimensions range from:

length 150 to 800 mm
diameter of the starting material 20 to 100 mm

Depending on the type of technology required:

heat treatment of the material (refining to the required strength)
turning
grinding
smoothing (rolling grooving)
induction hardening
milling of surfaces and grooves
milling and grinding of external straight and oblique teeth
surface treatment by quenching, nitriding