This pack of 10 metallic grey atoms are used typically to represent metals with tetrahedral coordination and is for extending your existing set or for replacing lost atoms. Each pack contains 10 balls with four holes in each ball arranged in a tetrahedral array. Each atom is 23 mm diameter.
Why would I need these? You could use them to represent a tetrahedral zinc atom in a compound such as [Zn(NH3)4]2+ or perhaps titanium in TiCl4.
The Molymod® system is the original, unique, dual-scale system of high quality low-cost molecular models. These enormously popular sets are ideal for students but are also used by scientists all over the world.