I installed one 200mi. before my fall
oil change. I left the magnet on after removing the filter,Cut the filter open & drained the can thoroughly.
Inside was a ghost like pattern of the magnet composed of ( I assume) iron particles that the filter had not removed.
I might note I have been using Fram HP1 filters & have switched to Wix with this change of
oil & filter. I also have always had a magnetic drain plug.
Craig