Other Characteristics Accuracy All Starrett-Webber gage blocks meet or exceed all known specifications. The flatness, parallelism and surface finish necessary to achieve the required accuracies are the same as or better than government requirements. St ability Starrett-Webber gage blocks do not change in size except through normal wear. Gage block stability is a characteristic that our Webber Gage Division has mastered with over eighty years of experience. Our gage blocks withstand the test of time. Hardness Steel blocks have a Rockwell "C" hardness of approximately 64-65. Chromium Carbide blocks have a Rockwell "C" hardness of 71-73, with an unusually fine, hard grain structure, giving them exceptional resistance to wear and abrasion. Thermal Conductivity and Coefficient of Expansion These are not important considerations when measurements are taken in temperature-controlled environments. This is primarily done when measuring to microinches or microns. On the shop floor, where precision measurements are rarely finer than .0002" or 0.005mm, the coefficient of expansion of steel, chromium carbide and ceramic is so close as to be negligible. Thermal conductivity is important on the shop floor. However, because it takes time for a gage block to move to the same temperature as the workpiece, we recommend setting the gage block on a heat sink such as a large mass of metal that is at the shop environment temperature. Gage Blocks – Major Product Characteristics Precision gage blocks are the primary standards vital to dimensional quality control in the manufacture of parts. The four major characteristics that are necessary for a precision gage block are accuracy, surface finish, wear resistance and dimensional stability. Other factors are corrosion resistance, hardness, thermal conductivity and coefficient of expansion. The base material used for gage blocks is crucial in meeting the above criteria. While many materials have been tried, the major types available today are: • Traditional high-grade steel gage blocks, which are generally used in shop floor environments • Tungsten Carbide gage blocks, which have the advantage of being harder and longer wearing than steel (Not available from Starrett-Webber) • Ceramic gage blocks will outwear regular steel and will not corrode • Chromium Carbide gage blocks are considered the top of the line; the finest available. They outwear regular steel and ceramic. In addition, they will not corrode, are very stable and accurate, and have exceptional "wringing" qualities. croblox® Chromium Carbide is the superior gage block material. The reason that our Webber Gage Division emphasizes gage blocks made from Chromium Carbide is because they are the most stable measuring devices ever developed. No one in the world except Starrett-Webber has produced the accuracy and stabilityofourcrobloxGrandMasters.Theywereproducedin1955ofChromium Carbide material to an accuracy within one millionth of an inch (.0000254mm) and have been checked periodically by the U.S. National Bureau of Standards and the U.S. National Institute of Standards and Technology (NIST) and have remained stable over this period. Precision Gage Blocks, St andard Reference Bars 376 S t arrett -W ebber G age B locks