Refer to the pictures I've posted there.
Essentially the little red silicone rings come with Monster branded IEM tips packages. Not sure if all of them have it or only specific packages. Or if they sell them individually.
What they are, is a sleeve for namely Shure IEMs (and others with thin nozzles) so you can use standard IEM tips.
That said, the sleeve doesn't necessarily make the nozzle size exactly like a typical nozzle, but almost. Especially in the BA200's case. To boot, standard IEM tips tend to have different bore size, so all in all some tips will still fit a bit too loosely.
Basically it opens the choice to most existing IEM tips on the market. Deep insertion remains something difficult to do with those on though (or at least for those of us with smaller ear canals). I've yet to try with standard bore size dual/triple flange due to simply not having any, and also how I usually can't stand anything longer than single flange... but the larger opening could possibly open up the mids.