This is a wire-screen filter from an engine dyno, and it's easy to see how much "stuff" floats through the oiling system on a new engine build. This is the accumulation after KT Engine Development ran two new race engines on its dyno. (The screen is usually cleaned after every dyno session, but it wasn't cleaned this time so that the buildup would be easier to see.) Much of what you see here is lint from cleaning rags and other harmless matter. The amount of material that gets trapped in a filter should dwindle to virtually nothing in a healthy engine after the break-in process is complete.