an inch. For instance, in figure 2-23, the last digit of the series number is 4; therefore, this bolt is 4/16 of an inch  (1/4  of  an  inch)  in  diameter.  In  the  case  of  a series number ending in 0, for instance AN30, the 0 stands for 10, and the bolt has a diameter of 10/16 of an inch (5/8 of an inch). Refer again to figure 2-23, and observe that a dash follows  the  series  number.  When  used  in  the  part numbers for general-purpose AN bolts, clevis bolts, and eyebolts, this dash indicates that the bolt is made of carbon steel. With these types of bolts, the letter  C, used in place of the dash, means corrosion-resistant steel. The letter D means 2017 aluminum alloy. The letters DD stand for 2024 aluminum alloy. For some bolts of this type, a letter  H is  used  with  these  letters or with the dash. If it is so used, the letter  H shows that the bolt has been drilled for safetying. Next,  observe  the  number  20  that  follows  the dash. This is called the dash number. It represents the bolt’s grip (as taken from special tables). In this instance the number 20 stands for a bolt that is 2 1/32 inches  long. The last character in the AN number shown in figure 2-23 is the letter A. This signifies that the bolt is not drilled for cotter pin safetying. If no letter were used after the dash number, the bolt shank would be drilled  for  safetying. NAS  Part  Number.—Another  series  of  bolts used   in   aircraft   construction   is   the   NAS.   See figure  2-24. In  considering  the  NAS  144-25  bolt (special  internal-wrenching  type),  observe  that  the bolt identification code starts with the letters  NAS. Next, the series has a three-digit number, 144, The first two digits (14) show the class of the bolt. The next   number   (4)   indicates   the   bolt   diameter   in sixteenths of an inch. The dash number (25) indicates bolt grip in sixteenths of an inch. Figure 2-24.—NAS bolt part number breakdown. Figure 2-25.—MS bolt part number breakdown. MS Part Number.—MS is another series of bolts used  in  aircraft  construction.  In  the  part  number shown in figure 2-25, the MS indicates that the bolt is a Military Standard bolt. The series number (20004) indicates the bolt class and diameter in sixteenths of an inch (internal-wrenching, 1/4-inch diameter). The letter H before the dash number indicates that the bolt has a drilled head for safetying. The dash number (9) indicates the bolt grip in sixteenths of an inch. Nuts Aircraft nuts differ in design and material, just as bolts do, because they are designed to do a specific job with the bolt. For instance, some of the nuts are made  of  cadmium-plated  carbon  steel,  stainless  steel, brass, or aluminum alloy. The type of metal used is not identified by markings on the nuts themselves. Instead,  the  material  must  be  recognized  from  the luster of the metal. Nuts also differ greatly in size and shape. In spite of  these  many  and  varied  differences,  they  all  fall under  one  of  two  general  groups:  self-locking  and nonself-locking. Nuts are further divided into types such as plain nuts, castle nuts, check nuts, plate nuts, channel nuts, barrel nuts, internal-wrenching nuts, external-wrenching  nuts,  shear  nuts,  sheet  spring nuts, wing nuts, and Klincher locknuts. NONSELF-LOCKING  NUTS.—Nonself-locking nuts require the use of a separate locking device for security of installation. There  are  several  types  of these  locking  devices  mentioned  in  the  following paragraphs in connection with the nuts on which they are used. Since no single locking device can be used with all types of nonself-locking nuts, you must select one suitable for the type of nut being used. SELF-LOCKING   NUTS.—Self-locking    nuts provide tight connections that will not loosen under vibrations. Self-locking  nuts  approved  for  use  on aircraft meet critical strength, corrosion-resistance, 2-19