Scientific studies of borate glasses tend to focus on alkali borates, which can be made over a wide and continuous composition range. Contrastingly, metal borates have a wide immiscibility region at low to medium metal content in which glasses cannot readily be made. Nevertheless, metal borate glasses are more important for many potential applications. Metal borates, however, can be made as glasses at the metaborate composition, and we will investigate the structure of 9 different metal metaborates. We will investigate the likely relation between the fraction of 4-coordinated boron atoms and the cation field strength of the metal cations.