These are constructed from durable spring steel and are black oxide treated for extra strength. Contents: 3mm x 20, 4mm x 10, 5mm x 15, 6mm x 25, 8mmx 15, 9mm x 20, 11mm x 15, 12mm x 15, 13mm x 25, 14mm x 15, 16mm x 20, 19mm x 25, 20mm x 15, 22.5mm x 20, 25mm x 15, 26mm x 15, 28mm x 10, 32mm x 5.