Here is a link to a nice discussion on Stelvin type closures, among others. I knew New Zealand wines were heading this direction and thought this presentation was very well done.
These closures require specialed equipment, they are not comparable to the standard plastic screwcaps commonly available to home winemakers.
I thought some of you might be interested in them, so here is the link:
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(I ordered some Altecs for testing so am back into looking at closures again. So far I like the twin tops and Nomacorcs better than Supremecorc, Guardian and aggomerated.) Joe