?? Meets/exceeds: DIN 912, ISO 4762?? Material of Screws: 12.9 grade alloy steel, hardness: HRC 39-44, tensile strength: 1220N/mm²?? Screws Rust proof: black oxide finish, covered with anti-rust oil?? These screws and Hex Key Wrench come in a separated girds storage case [ Sizes ] ------------[ Thread Length ]-----[ Total Length ]/b> M4 x 20mm-----------20mm--------------24mm M4 x 25mm-----------25mm--------------29mm M4 x 30mm-----------30mm--------------34mm M4 x 35mm-----------35mm--------------39mm M4 x 40mm-----------40mm--------------44mm Package Contains:/b> M4 x 20mm---------10 Pcs M4 x 25mm---------10 Pcs M4 x 30mm---------10 Pcs M4 x 35mm---------10 Pcs M4 x 40mm---------10 Pcs Hex Key Wrench------1 Pcs Total: 51 Pcs About Hex Socket Drives Hex Socket drives, also known as Internal hex drives, have a hexagonal hole in the center that requires an Allen key, also known as a hex key or Allen wrench About Socket Cap Head Socket Cap Head screws, also known as Allen head screws, have a recessed drive, and are commonly used when there is not enough clearance for a conventional wrench or socket. They are fastened with an Allen wrench, which is also called a hex wrench or hex key