This is a package of twelve 2.5mm Ceramic Nitride Pro Series Differential Balls from ACER Racing. FEATURES: Ceramic Nitride construction, black in color Grade 5 diamond polished for low rotational mass 79% lighter than Tungsten Carbide and stronger Each pack is matched for consistent concentricity, roundness and smoothness Will not melt or shatter under extreme racing conditions INCLUDES: Twelve 2.5mm diameter Ceramic Differential Balls REQUIRES: Installation SPECS: Diameter: 2.5mm tlw 6/5/07 ir/jxs