European Truck Part Name Question

I recently picked up an older Italeri 1/24 Mercedes-Benz truck kit. This kit has round parts that remind me of washers and that fit over the lug nuts and studs on the front wheels like a spacer; there are holes in the parts so the nuts on a real truck can be removed/reapplied, but the part seems to keep the nuts & studs from being damaged or from damaging anything they come in contact with. These parts are often seen on the front wheels of heavy European trucks, but are almost unheard of in North America. Can anyone tell me the proper name of these parts?
Thanks,
Tony Hodun
Ohio, USA