mishar

5 doesn't have that centering ring so the wheel is centered by the hub. 15 is thick enough to cover the hub and have a centering ring. 10 is nowhere, but those guys managed by that sloped segment to overcome that problem.

I am Audi Gury. VW just apprentice. Check if they are conical.

For the washer test you may need some duct tape to hold them in place.

aTOMic

I think I'll make three wheel hangers; one for each car and one for the toolbox. Then I won't need to muck about with duct tape.

I called the company "Meister" and spoke at length to Mister Meister himself. He aid pretty much what you day above regarding the 10mm, but they specialize in VWAG to VWAG and he said the bevel has to be just right. (and they, of course, make 'em jut right).
Then I saw these, 10mm and just for my VW:
http://www.ebay.com/itm/Bulldog-10mm-20mm-5x112mm-57-1mm-VW-Passat-1996-2012-TUV-/271451722427?pt=Apparel_Merchandise&vxp=mtr&hash=item3f33c892bb
surprisingly they are TÜV § 19.3 certified; one would think the correct bolts would be a necessary component for that honor.

Decisions, decisions

mishar

It is not clear (to me) if they are 10 or 20 mm. Looking at the picture I would say neither. Besides that they are twice more money and bolts are not included. Not much engineering that it has to be German.