Black Square 11/16" Corozo Button, Five Squares Tagua Nut "Vegetable Ivory", 17mm #SK-521
Square button with four square holes. It's almost 1/8" thick and slightly raised - 'pillowed' in the center. The back is flat. Silky finish with a bit of sheen, rich true black sustainable corozo/tagua nut. $1.70 each
11/16" Diameter/17mm. Also available smaller, 9/16", in a separate listing. They match.
...and in other colors in other listings.
Vegetable Ivory/Tagua/Corozo: Click here or here for wikipedia articles about this tropical palm tree nut. Tagua has been used for making buttons since the 1880's, before plastic. It carves and dyes very well, is extremely durable, and looks better than plastic; not as shiny.