Vintage Flat Glass Upper Plate PI-60 ??-60 About 1980 Measuring Tool. The flat glass plates are intended for checking by interference methods the lap-ability and planarity of the measuring planes of plane-parallel end standards of the metre, gauges, measuring instruments and tools. These plates are widely used in various applications, for example, in instrument making, tool making, mechanical engineering and many other industries. The plates are produced in two modifications: lower and upper. The lower (bearing) plates are used for checking the lap-ability and planarity of the measuring surfaces of end standards of the metre, gauges, measuring instruments and tools. The upper plates are used for measuring plane-parallel end standards of the metre by the interference method. diameter of upper plate - 60 mm deviations of working surfaces from planarity of plates of the 2nd class of accuracy: 0.3 of interference band local deviations from planarity of working surface, not over: 0.3 of interference band overall dimension (mm) - D60x20 weight (kg) - 0.143 Will be shipped from Europe by Air Mail International priority mail. Thanks for looking I will ship Worldwide. PayPal only. No returns Powered by Turbo Lister Powered by Turbo Lister