The Nikon 400mm 2.8 has a lens hood that costs $400. For this price, you would think they use pretty solid parts, but there is a block that a thumbscrew goes into that’s actually hard plastic. If your lens is in a backpack with the hood attached, this retaining screw will strip.
I have read many forum posts where people begrudgingly REPLACED THE ENTIRE HOOD because of this. People said they contacted Nikon directly and were told there are no replacement parts.
After contacting Nikon, I would like anyone googling for a solution to know that you can order the parts from Nikon, the parts and numbers are pictured above. Contact the Nikon Parts Service at: 310-414-5121