Vervelles are small metal staples used in Medieval armour to attach an aventail to a helmet. A leather cord would be woven through the top row of rings and the vervelles, securing the two together.
Bibliography
Edge, David; John Miles Paddock (1993) [1988]. Arms & Armor of the Medieval Knight (Crescent Books reprint ed.). New York: Crescent Books. ISBN 0-517-10319-2.