Re-Stocked Black Corozo Button, "Five Squares" Pillow-Top, Tagua Nut, 9/16" / 15mm #SK-513
Square button with four square holes. It's almost 1/8" thick but then slightly raised - 'pillowed' in the center. Silky finish with a bit of sheen, rich true black sustainable corozo/tagua nut. Sold per button. 9/16" Diameter, just over 1/2". Also available larger, 11/16", in a separate listing. They match.
...and in other colors in other listings.
Vegetable Ivory/Tagua/Corozo, 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. Machine wash and dry, but not too hot.