Each pack contains assortment of 12 flat pink and purple orbitals to represent p- and π-orbitals (6 pink, 6 purple). Each fits directly into an appropriate hole on atoms. You might use these to represent the bonding in ethene or benzene in conjunction with the five hole carbon atoms available separately. 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. This item is for extending an existing set or for replacing lost parts.