Review on Optical Glass Lens with Ground, Beveled Edges - Eisco Labs Top Spinning Base, 3" (75mm) Surface, Double Concave, 200mm Focal Length, Optically True by Shane Jenkins

. This lens is suitable for a gyroscope, but to advertise it as PERFECT for this purpose is an exaggeration. This depends on your vertex and the type of rotation you want. This 200mm lens is slightly more curved than the Foreverspin base, resulting in a greater tendency to spin or wobble. Medium density glass and not as hard as Foreverspin backing. An advantage of this lens is that at the end of the rotation, the extra curvature prevents the vertex from rotating over the edge. The build quality is average and not stable. I bought 2 of these, one was 2mm larger in diameter, 1mm thicker; Edge grind varies and is not polished. A flatter surface offers better spin for me. I bought another 300mm concave lens to compare (flatter, less curvature) and it offers better rotation for me but is harder to find with a diameter of this size or larger.