Racers are upgrading their steel differential balls to Tungsten Carbide balls. ACER Racing's Tungsten Carbide balls are unsurpassed by any other Tungsten Carbide ball in quality, durability and resistance against degradation, wear, shock, and impact. Unlike steel balls ACER Racing's Carbide balls can last race after race after race without being replaced. These are the hardest and smoothest Carbide balls available. Each set of balls is matched for consistent concentricity and quality control checked. All balls are Grade 10 (not the lower Grade 25 that some others use) AVAILABLE FOR VIRTUALLY EVERY POPULAR RC KIT!