World Champion ACER Racing 3/16x3/8x1/8 Ceramic Ball Bearing. This is a 3/16x3/8 ceramic ball bearing also known as a size R166 ball bearing. Diamond polished Silicon Nitride (Si3N4) Balls, HSR cage technology and sealed on both sides. Lubricated with lightweight and 100% synthetic ACER Racing SIN Oil instead of thick grease for super fast and super smooth action.