.../... the exact content of the thrust arm repair kit (A1103501475)
Note that the large dia trailing arm bolt, key width 36mm, supplied nowadays is made with a flat face.
I save and refurbish the originals; I think it is a nice touch and makes quite a visible difference there on the rear axle.
I suppose, the "hollowed out" original version bolt is too expensive to produce today. See comparison photo attached, "current vs. original".
Note, I borrowed the pic "Trailing arm bolt", not my car. The bolt should be tightened to >300NM (some 225 lbft); the thin metal washer shall then be folded on one hex side, to lock the bolt in position.
To remove the bolt, a tool such as shown on attached pic is useful
Note No 2: Be sure to only fully fasten these four bolts once the car is on its wheels; suspension in "normal" position, otherwise you introduce tension in the rubber, gives inferior ride quality and short life for rubber components...
/Hans S