Section 39.573. Test for clear glass lenses

A spherical steel ball 16 grams (0.565 ounces) in weight approximately 1.59 centimeters (0.625 inches) in diameter (weight shall be correct within 20%), shall be dropped once from a height of one meter (39.37 inches) on the center of the horizontal outer surface of the lens when held in a frame. The lens shall be supported by the rim of the frame only, on a rubber washer of 6.5 millimeters (0.25 inches) thick, held upon the top of a board or block of wood. If one out of six lenses that are tested is fractured in such a way that a fragment of glass weighing more than 25 milligrams leaves the bottom surface, four more lenses shall be tested, and if one of these lenses fractures in the manner described above, the lot shall be rejected.