A flange nut delivers a created-in washer (flange) that distributes the clamping load over a wider area than a regular lock nut. The design isn't going to need a flat washer and is particularly the better choice for an outsized or slotted hole. JBugs has become promoting classic VW areas https://peterq322ilm5.shoutmyblog.com/27875033/car-nuts-can-be-fun-for-anyone