Hardware Structural Analysis

Preferred Torque Callouts

The information contained herein is based on 50% ultimate tensile strength of series 300 CRES@80 KSI and A286 CRES@160 KSI, published tensile area for each screw size and pitch, and Shigley's 5T/D relationship. Here's a link to another user friendly torque chart.
 Screw Size                    Torque +/- 10 %
  		      300 Series CRES          A286 CRES
			(@80 KSI)             (@ 160 KSI)

 #0(.060)  -80UNF       14.0 in-oz            --------
 #1(.073)  -72UNF        ---------           26.0 in-oz
 #2(.086)  -56UNC        2.5 in-lb            5.1 in-lb
 #4(.112)  -40UNC        5.4 in-lb           10.8 in-lb
 #6(.138)  -32UNC       10.0 in-lb           20.1 in-lb
 #8(.164)  -32UNC       18.4 in-lb           36.7 in-lb
 #10(.190) -32UNF       30.4 in-lb           60.8 in-lb
*1/4(.250) -20UNC       63.6 in-lb          127.0 in-lb
 1/4(.250) -28UNC       72.8 in-lb          146.0 in-lb
*5/16(.312)-18UNC      131.0 in-lb          262.0 in-lb
 5/16(.312)-24UNF      145.0 in-lb          290.0 in-lb
*3/8(.375) -16UNC      232.0 in-lb          465.0 in-lb
 3/8(.375) -24UNF      263.0 in-lb          527.0 in-lb
              * non preferred pitch sizes.

Preloading Bolts and Shigley's 5T/D Formula

If your using self-locking screws and/or nuts you should add, "above prevailing torque", to your torque note. Example: TORQUE 5.4 PLUS OR MINUS .6 IN LBS, ABOVE PREVAILING TORQUE. See Figure 1 below, for some simple calculations relating to this.
Figure 1

Optimum Lug Design Utilizes the E/D Relationship

Normally, 1 1/2 D is adequate structurally. See Figure 2, below.

Figure 2