The Cleco fastener consists of a steel cylinder body with a  plunger on the top, a spring, a pair of step-cut locks, and a  spreader bar. These fasteners come in six different sizes:  3 ⁄ 32,  1 ⁄ 8,  5 ⁄ 32,  3 ⁄ 16,  1 ⁄ 4, and  3 ⁄ 8-inch in diameter with the size stamped on  the fastener. Color coding allows for easy size recognition. A  special type of plier fits the six different sizes. When installed  correctly, the reusable Cleco fastener keeps the holes in the  separate sheets aligned. Hex nut and wing nut fasteners are used to temporarily fasten  sheets of metal when higher clamp up pressure is required.  [Figure 4-73]  Hex nut fasteners provide up to 300 pounds  of clamping force with the advantage of quick installation  and removal with a hex nut runner. Wing nut sheet metal  fasteners, characterized by wing shaped protrusions, not only  provide a consistent clamping force from 0 to 300 pounds, but  the aircraft technician can turn and tighten these fasteners by  hand. Cleco hex nut fasteners are identical to Cleco wing nut  fasteners, but the Cleco hex nut can be used with pneumatic  Cleco installers. Aluminum alloys are the most frequently encountered type  of sheet metal in aircraft repair. AC 43.13-1 Chapter 4, Metal  Structure, Welding, and Brazing; Section 1, Identification  of Metals (as revised) provides an in-depth discussion of  all metal types. This section describes the aluminum alloys  used in the forming processes discussed in the remainder of  the chapter.  In its pure state, aluminum is lightweight, lustrous, and  corrosion resistant. The thermal conductivity of aluminum  is very high. It is ductile, malleable, and nonmagnetic. When  combined with various percentages of other metals (generally  copper, manganese, and magnesium), aluminum alloys that  are used in aircraft construction are formed. Aluminum  alloys are lightweight and strong. They do not possess the  corrosion resistance of pure aluminum and are usually treated  Aluminum Alloys Hex Nut and Wing Nut Temporary Sheet Fasteners Cleco Fasteners to prevent deterioration. Alclad™ aluminum is an aluminum  alloy with a protective cladding of aluminum to improve its  corrosion resistance. To provide a visual means for identifying the various  grades of aluminum and aluminum alloys, aluminum stock  is usually marked with symbols such as a Government  Specification Number, the temper or condition furnished,  or the commercial code marking. Plate and sheet are usually  marked with specification numbers or code markings in  rows approximately five inches apart. Tubes, bars, rods,  and extruded shapes are marked with specification numbers  or code markings at intervals of three to five feet along the  length of each piece. The commercial code marking consists of a number  that identifies the particular composition of the alloy.  Additionally, letter suffixes designate the basic temper  designations and subdivisions of aluminum alloys. The aluminum and various aluminum alloys used in aircraft  repair and construction are as follows: •  Aluminum designated by the symbol 1100 is used  where strength is not an important factor, but where  weight economy and corrosion resistance are desired.  This aluminum is used for fuel tanks, cowlings, and oil  tanks. It is also used for repairing wingtips and tanks.  This material is weldable. •  Alloy 3003 is similar to 1100 and is generally used  for the same purposes. It contains a small percentage  of magnesium and is stronger and harder than  1100 aluminum. •  Alloy 2014 is used for heavy-duty forgings, plates,  extrusions for aircraft fittings, wheels, and major  structural components. This alloy is often used for  applications requiring high strength and hardness, as  well as for service at elevated temperatures. •  Alloy 2017 is used for rivets. This material is now in  limited use. •  Alloy 2024, with or without Alclad™ coating, is  used for aircraft structures, rivets, hardware, machine  screw products, and other miscellaneous structural  applications. In addition, this alloy is commonly  used for heat-treated parts, airfoil and fuselage skins,  extrusions, and fittings. •  Alloy 2025 is used extensively for propeller blades. •  Alloy 2219 is used for fuel tanks, aircraft skin, and  structural components. This material has high fracture  toughness and is readily weldable. Alloy 2219 is also  highly resistant to stress corrosion cracking. Figure 4-73.  Hex nut fastener. 4-30