First set includes long arm hex keys in sizes: .050", 1/16", 5/64", 3/32", 7/64", 1/8", 9/64", 5/32", 3/16", 7/32", 1/4", 5/16", and 3/8". Second set includes short arm metric hex keys in sizes: 1.5mm, 2mm, 2.5mm, 3mm, 4mm, 5mm, 6mm, 8mm, and 10mm. Keys are made of 8650 chrome nickel alloy steel for maximum performance. Keys come in plastic holders that firmly retain the keys in sized marked holes.