TORQUE LIMITS AND STUD SELECTION CONTINUED
TIGHTNENING METAL FASTENERS
When torquing a fastener, select a torque wrench whose range (Table 3) 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 to 100 will
be the most accurate from 25 to 75 Pound--Feet. The accuracy of readings will decrease as you approach 0
Pound--Feet or 100 Pound--Feet. The following ranges (Table 3) are based on this principle.
Table 3. TORQUE RANGES
MOST EFFECTIVE RANGE
FASTNENER 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 4), which is a measure of 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 4 THREAD CLASSES AND DESCRIPTION
Thread patterns are designed as follows:
Note: Unless followed with LH (e.g. ¾--1OUNC--2A--LH), threads are right hand.