I had 2 fenders on my VS4-10 snap where they are bolted to the chassis with 2 bolt next to each other, near the bumpers.
Maybe I screwed them in too tight, maybe it's a weak point in the design.
These washers are supposed to reinforce that area.
Print 4, one for each corner of your truck.
Basically it's 2 3mm holes, 8mm apart and a bevelled edge for extra fanciness.
Regular version is 1.2mm thick, the thick version is 2mm.
No additional hardware required, the stock bolts are long enough.