Ruby Sapphire

• Al ₂O₃
• Hexagonale rhomboedrique
• Density 3,99 - 3,98
• Fusion Temperature 2050°C
• Thermal expansion 5,4 x 10-6/°C face perp. axe C
• 6,2 x 10-6/°C face paral. axe C
• Hardness Mohs 9
• Hardness Knoop 1800 face perp. axe C
• 2200 face paral. axe C
• Refractive index nd 1.760 face perp. axe C
• 1,769 face paral. axe C
• Dispersion factor 0.011

• Basic diameter: The size ordered which is the basis to which the basic diameter tolerances apply. The basic diameter is specified by a fraction plus a decimal or a decimal only to the sixth place. (example: 1/4'' + .0002'' or .2502'' - 15/64'' + .0003'' or .234675'').
• Basic diameter tolerance: The maximum allowable deviation of any ball diameter from the basic diameter, in any shipments to fill orders for that basic diameter.
• Diameter tolerance per ball: The permissible difference between the largest diameter and the smallest diameter measurable on one ball.
• Diameter tolerance per unit container: The permissible range of the average diameters of the individuals balls within any one unit container.
• Grade: The numerical value of the diameter tolerance per ball expressed in a millionth of an inch.
• Marking Increments: The standard unit steps in a millionth of an inch used to express the specific diameter. Some materials prevent us from obtaining a better result of tolerance than those obtained at level 10. On the other hand, some materials, mainly ceramics, make it possible to obtain dimensions with a level 4 or 5 , RA is then higher than in the above table.