wiring harness to fuse box: how to tighten the nut

Hello,
I am trying to work out the following: I removed the wiring harness from the fuse box on the engine compartment side. The wiring harness has three sets of plugs. When they are all fitted together, the middle set has a bolt that fixes all three to the fuse box.
Now, I have the threaded washer(?) which has three "spikes" to stop it from rotating when the bolt is tightened into the washer.
I can't remember how to install this washer so I can tighten the harness.
Anyone know where this washer goes?
Thanks.
Ian

Picture of bolt and washer? The washer I am assuming goes on the bolt other side of plastic for the washer so the bolt is retained in the plastic. Make any sense? Good Luck. Not sure why the bolt came off.

IIRC the bolt is fixed in place (or should be), as said above could that washer be the lock that holds the bolt in place?