Impressive specifications, the best offered by research on materials, thanks to an exclusive process of molecular transformation, OPUS ceramic zircon offers a mechanical strength which preserves its entirety in case of accident fall. - excellent abrasion resistance, with wear up to 10 times less compared to hardened steel. - excellent corrosion resistance - low thermal conductivity - high dimensional stability - hand-lapped surfaces Every block has a serial number. Dimensional tolerance conformed to DIN 861, ISO 3650 and BS 4311 standards. Compositions available in wooden box, or singles, always with UKAS calibration certificate in C class on 5 points included in the price. Available, on demand, different compositions and single box.