Yesterday when changing oil on a Ducati 848 EVO 2012 motorcycle after about 4000km (which is soon enough considering it went through a track day) I noticed a small concentration of microscopic metal shavings on the magnetic oil drain plug. These metal particles size is small enough to render them invisible to the naked eye and only can be seen as magnetized "tentacles" on the magnet or by coloring a paper gray if wiped out. I understand that these particles are actually ground metal from areas where friction applies inside the engine but i was wondering which are the engine parts that most contribute on their creation. Is there a maximum accepted size for these metallic particles before they become catastrophic for the engine?
My rep isn't high enough to just leave this as a comment so I hope this answers your question. There are a lot of reasons you could have shavings in your oil all the way from impending catastrophic engine failure to the mundane friction based issue as you mentioned. There are times where shavings may even be expected, such as engine break in https://www.motorcyclistonline.com/how-much-debris-is-normal-in-oil-after-motorcycle-break-in/ .
The shavings on their own will only tell you part of the issue, it may be beneficial to consider a UOA (used oil analysis). There are companies that you can send an oil sample to and they will analyze the content of it and provide you with a description of what they see along with what you may expect in the near future with your engine. One such company I know of is Blackstone (www.blackstone-labs.com) but I'm sure there are countless others. From their website:
"Oil analysis is a quick, nondestructive way to gauge the health of an engine by looking at what's in the oil. People use oil analysis for different reasons: to see if there are any problems developing, to see if their oil is working well in the engine, and to see if they can run longer oil changes."
And to state the obvious as well since you mentioned a track day. Those kinds of events, besides being a ton of fun, put your engine into performance ranges you generally don't see on public roads which can cause wear/tear at a higher rate.
I would call them particles , not shaving since they are so small. They are steel being magnetic , so not from plain bearings and unlikely to be from rolling element bearings ( steel). Not much info to speculate from, but it doesn't sound like there is necessarily a problem. As answered , a Blackstone analysis of the used oil would give more clue if there is a problem ; as I remember Blackstone gives general info on the significance of Cu, Sn, Pb , Fe, etc.