Creating an outline of an image

Hi, I know there was a recent thread about creating outlines of images which was resolved with a good tutorial but it doesnt seem to be working for the image I'm trying to do. My image is EXTREMELY simple but I'm asking for help because I have no skill the the art field and I need this to look professionally done. If anyone can help me figure out how to make outlines of this image any help would be greatly appreciated.

Do you need just the outline of the outer edge, or do you need a line drawing?

Just this one image??

just this one image... honestly i'm not sure what a line drawing is but I think that is what I'm trying to accomplish, not just an outline it needs to be more identifiable as a lock. I'm dying here spending 4 hours trying to do this is really ruining my day.