Decoupler shaft?

[Koda1228]

What is the shaft called that the decoupler pulley threads onto? My belt snapped and broke that shaft off clean with the pulley. I read a few places that the seal behind the decoupler pulley is the crankshaft seal but that just wouldn’t make any sense of that was the case cause why would the crankshaft lead to the alternator, through the time chain cover, to a pulley, please help I’ve been researching this for almost 6 hours today and haven’t found a thing...