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Well maybe you should look at what is used on aircraft instead making assumptions. While there are mil-spec lock washers that were used on some aircraft, they are never used in an area where safety could be compromised by them coming loose. In safety critical areas, either castle nuts and cotter pins are used or safety wire is used. Nylon insert nuts are now the preferred choice in all instances where castle nuts and/or safety wired is not required. My own feeling is that if it is important enough to need a lock washer, it is important enough to use a high quality nylon locking nut.
If however you are talking about holding pieces of plastic together for cosmetic panels, you can use all the plastic push fastners you want.
On another post you commented on the "single" use of the nylon insert nuts and this may be correct if you are using the common cheap Home- Depot made in China hardware. I have found that aircraft grade nylon insert nuts will still provide a firm tight hold after two or three cycles. I wouldn't recommend them for more than that though.