Clip on sunglasses protect your eyes from summer sun or winter glare when you are wearing regular glasses.
Simply clip onto your spectacles using a sliding action and springed arms firmly hold the sun filtering lenses in place.
This is clever, but the clip on sunglasses hold a surprise.
The filtering lenses are mounted on hinges so that you can flip them out of the way when not needed.
Very handy.
Some people also use clip on sunglasses when driving.
