TM-9-2350-311-20-1 Maintenance Manual for Volume 1 M109 Hull Download
Page 1161 of 1275
F-3 TIGHTENING METAL FASTENERS When torquing a fastener, select a torque wrench whose range (Table F-2) fits the required torque value. A torque wrench is most accurate from 25% to 75% of its stated range. A torque wrench with a stated range of 0-100 Ib-ft (0-1 36 N.m) will be most accurate from 25-75 lb-ft (34-102 N-m). Accuracy of readings will decrease as you approach 0 Ib-ft (0 N·m) or 100 lb-ft (136 N·m). The following ranges (Table F-2) are based on this principle. TABLE F-2 TORQUE RANGES STATED RANGE MOST EFFECTIVE RANGE F-4 FASTENER SIZE AND THREAD PATTERN Threaded fasteners are categorized according to diameter of fastener shank. Thread styles are divided into broad groups, the two most common ranges being coarse (Unified Coarse-UNC) and fine (Unified Fine-UNF). These groups are defined by the number of threads per in. on the bolt shanks. In addition, threads are categorized by thread class (Table F-3), which is a measure of the degree of fit between the threads of the bolt or screw (external threads) and the threads of the attaching nut or tapped hole (internal threads). The most common thread class for bolts and screws is class 2. TABLE F-3 THREAD CLASSES AND DESCRIPTION EXTERNAL INTERNAL FIT 1A 1B Loose fit 2A 2B Medium fit 3A 3B Close fit Thread patterns are designed as follows: NOTE Unless followed with -LH (e.g., 3/4-1 OUNC-2A-LH), threads are right-hand. TM9-2350-311-20-1 F-4