[Dukedesmo]

To add, as per Utopia's post mine has no channel/saddle washer under the nut but then I built mine from a frame and swingarm sourced separately so it is not OEM and I have no idea how Ducati did it.

I too have a washer under both nut and bolt head, I have a stainless bolt/nut with plenty of copper grease on the threads to prevent binding plus, I know it's free as it's been off many a time - including a few months back when I replaced the swingarm.