[quote=bobdadruma;1243716]The lug nut would only fall out if you removed the plastic plug and the tension rod from the lug casing.
The shoulder tube of the plastic plug will hold the lug nut in place.[/QUOTEesthetic
So its not just aesthetic, it holds the lug nut in place.
Tho we're hearing that without the plastic piece, the rod/tuning/function would not be effected.
We're then to assume the lug nut jams up against the metal casing of the lug when tension is applied, or in the case of a proper design there's a channel in the metal part of the lug that secures the lug nut during tuning.
It's sole purpose is to hold the barrel nut or threaded tube (lug nut) into the lug.
Or as Harvestdrum
sez: "It appears its designed like this incase the barrel nut gets damaged and needing replacement."
So an access hole to the lug nut on the outside, the back (shell side) of the lug from the pic shows the lug nut is not acessible from the back, the plastic part is basically a 'lug nut access hole cover' is what were getting its 'function' is.