Newmei,
From a mechanic's perspective, it's impossible to tell you about what you found without seeing it. However, generally speaking, the only thing your oil screen will actually screen out is anything big enough to have a part number. Smaller than that, and it bypasses the oil screen anyway (figuratively speaking).
You can do yourself (and your engine) a favor by purchasing and maintaining an STC'd full-flow spin-on filter adaptor.
The type of metal you found is important. The first thing you want to determine when investigating metal chips or particles is weather or not the material is ferrous. Use a magnet. If it sticks, it's ferrous. This gives you a start in determining what you have. From there, it becomes a process of elimination. In your case, you've determined it's ferrous; now you need to determine what it is.
It's important to remember that you've located one piece. There are almost certainly more pieces. I would run your oil through a screen when it's drained, to see what else comes out. It may or may not have all made it to your oil screen on the engine. Use a piece of household screen to sift the oil for other bits of debris as it drains into a bucket. This generally works best if the screen s in a funnel, or similiar device. You can put it in a cut open oil can, and run it through that, barring anything else.
Where there is one piece, you often will find more. The question arises what will happen if these parts go through the oil pump gearing, or arrive at a bearing journal...or get stuck in an oil galley. Nothing good can come of it. It sounds as though you may have part of a gear tooth there.
Change your oil every 50 hours or three months, whichever comes first. If you don't fly a minute in three months, change the oil anyway. I prefer 25 hour oil changes in airplanes.
Start on a regular oil analysis program. Take a sample every oil change, and submit it. Keep a compilation of the reports. A single report won't necessarily tell you anything about the engine, but a trend and a baseline will. Get to know what the engine is producing, and check for changes. This is one of the single most valueable things you can do for that engine as an owner, after regularly changing the oil, and operating the engine responsibly.
As for carbon, you'll see a change in carbon in the filter if you've changed types or grades of oil, or have switched from mineral to multigrade, etc. If you're going from straightweight to multigrade, be prepared to begin seeing more deposits.
Change your oil often, and ALWAYS take samples for submission. Good luck!!
