I think you win. At least I think your right. That is what it is. Actually it was a bolt hole cover I think.
But... the M8000 does not come with a Hawse Fairlead as is shown in that parts diagram where the holes would be plugged with part number 50.
The M8000 comes with a Roller Fairlead so this part is no longer applicable... it seems to me.
I guess its a left over parts supply or parts application from a time or place when a Hawse is supplied instead.
I think you're right. I just installed the Warn Steel Hawse Fairlead on mine and it included new bolts, washers, nuts and 2 round plastic caps to cover the bolt head in the fairlead for a clean finished look.
Mine are in the plastic bag in the miscelaneous extra parts can.