Traditionally tama are made of hard wood, turned on a lathe to create an hour-glass shape. In Japanese there is no “s” added to a word to create a plural so you have one tama, two tama, three tama etc.
As the tama weight is used in Kumihimo to exert force on the center (point of braiding), tama are weighted with lead. Japanese tama are generally 100gr, while US tama are usually 70gr, other weights are available. The weight of the tama is not as critical as the relationship between the total tama weight and the center-weight; the interaction of the two determine the length of the floats of thread in a braid and thus the density of the braid.
Recently, a line of tama was developed to better handle beaded braids. These tama have a deeper, broader profile to allow for larger-diameter elements.