Part of a Molecular Model kit Red Ball 2 Holes Holes at 90° from one another Pack of 10 Balls The red balls with 2 holes each (at 90° from one another) are parts of molecular model sets (which are used to provide a visual and kinesthetic aid for studying the structure and properties of various molecules). This 10 pack provides extras of this specific part (red balls with 2 holes each (at 90° from one another) for addition to a full set or to replace lost parts.