Recessed edges. Socket openings are designed to reduce fastener rounding. Chrome vanadium alloy steel construction for strength and durability. Polished nickel chrome plated finish resists corrosion. Large stamping for quick identification. Packaged on plastic slide rail for storage. Sizes: 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 1mm, 12mm, and 13mm.