And as Colorex mentioned, velcro is better. I'm told that rare earth magnets also do a really good job of holding the wing together without creating the (small amount of) drag that velcro does. I've got spare magnets, but I'll stick to the velcro for now methinks.
The one that I have here has long steel screws, they pass through two fibreglass collars in the interior of the wings themself to keep them straight and then fasten into two threaded steel collars that are fixed into the plywood that all the wires thread through inside the body of the fuselage. No plastic in either of the two I got, plane 1 or 2.
(I just had a look for the leftovers of the first plane. All that I could find was other areas of the plane, sorry I was going to photo and post.)