the guy who said "teeth" is correct
Correct term is "splines "
They are called cogs. Years ago, to distinguish between a smooth wheel and one that had teeth, the ones with teeth were called cogwheel. Cogs were not called teeth until around 1930.
TEETH somthing circular with teeth on is called a cog
splines, teeth, cogs, sprocket depending on the part and what country you are from