Hi, on offer is one of these Vintage Glass Convex Magnifier Lenses which measure 50 mm in diameter and are 14 mm deep approximately, they have a small rim on the outer edge enabling them to be mounted in a frame if needed. They are in good condition, some have very minor nibbles to the edges but they do not impede on the viewing area.  I have a number of these and will be pleased to combine postage if possible.