Very small antique steel studs. They have a blued steel base with cut steels rivetted individually through the base. The central boss goes through the base and attaches to a triangular stud type back … with just enough room for the fabric to go between the top and back. I had to cut the fabric away to remove one of these. I haven’t tried to remove the triangle on the back but this may be possible? Anyway, charming little steel buttons - or could be studs or embellishments. Definitely have age, probably early 19th century. Price is per button

Size 3/8” (0.9 cm)