Bolt/Nut combination is double secured against unwanted loosening:
There is tread patch pre-applied on the bolt and the nuts are “Fuji Lock”.
This is a metal ring which deforms during tightening and locks the nut secure.
In addition these Nuts are flanged to create a big contact area with the hub.
This is the Fuji lock principle explained however the bolt in this image is not flanged like our bolts are.