Dark Orange Square Corozo/Tagua "Five Squares Flat Pillow", 9/16" or 11/16"
Square button with four square holes. It's almost 1/8" thick but then slightly raised - 'pillowed' in the center, so it's not quite flat anymore. Bright pumpkin/dark orange color. Choose 9/16" or 11/16". $1.20 or $1.70 respectively.
Vegetable Ivory/Tagua/Corozo: Click here or here for wikipedia articles about this tropical palm tree nut. Tagua has been used for buttons since the 1880's, before plastic.