Lenses are pushed outward by the compression of air when closing the trunk. They need to hold well enough that closing the trunk will not cause them to pop out.
Stan, can I order another set of Euro lenses please? I have one old set of frames left that I want to restore as a spare. Or since I am in Oz is it easier to go direct to the supplier? I can't remember what I did last time. Thanks.And if you are wrong, I can sell more