TM 9-2815-250-24&P E-4.  TIGHTENING METAL FASTENERS (continued). Table E-3.  Torque Ranges STATED RANGE MOST EFFECTIVE RANGE 0-600 ft-lb 150-450 ft-lb 0-170 ft-lb 44-131 ft-lb 15-75 ft-lb 30-60 ft-lb E-5.  FASTENER SIZE AND THREAD PATTERN. Threaded  fasteners  are  categorized  according  to  diameter  of  the  fastener  shank.    Thread  styles  are  divided  into  broad groups,  the  two  most  common  being  coarse  (Unified  Coarse-UNC)  and  fine  (Unified  Fine-UNF).    These  groups  are defined by the number of threads per inch on the bolt shanks.  In addition, threads are categorized by thread class (Table E-4), which is a measure of the degree between threads of bolt or screw (external threads) and threads of the attaching nut or tapped hole (internal threads of the attaching nut or tapped hole) (internal threads).  The most common thread class for bolts and screws is Class 2. Table E-4.  Thread Classes and Description EXTERNAL INTERNAL INTERNAL 1A 1B LOOSE FIT 2A 2B MEDIUM FIT 3A 3B CLOSE FIT NOMINAL SIZE NO. THREADS/INCH THREAD SYMBOL THREAD CLASS 3/4 10 UNC 2A NOTE: Unless followed with -LH (e.g., 314-10 UNC-2A-LH), threads are right-hand. E-4