I think he means these rather than the rubber inserts in the diff itself:
They bolt under the diff mounts and act as bump stops, and I guess stop the diff falling off if the diff rubbers fail!
I plan to fit them to mine, but just via the hole in the middle, and won't bother bolting the two extra holes to the chassis.
I've seen them bolted on upside down on a Westfield build which makes them press against the diff giving it an
almost solid mounting:
