H-6. TORQUE TABLE (Cont.)
MOST EFFECTIVE RANGE
Installation and Torquing
Matching Nuts. Matching nuts require a minimum height (see page H-22) equal to the basic diameter
of the bolt. The same is true of tapped holes. In tapped softer materials, the depth of the tapped hole
should be 1-1/2 times the basic diameter of the bolt.
Thread Protrusion. In all installations, bolts, studs, and screws must extend through the nut at least a
length equivalent to two complete threads (see page H-22). This applies to both self-locking and plain
Torquing Self-Locking Nuts. To obtain the correct recommended torque value on self-locking nuts, the
nut must be tightened until it is one turn from the beginning of seating. At this point, if the torque is
less than 1/3 of the recommended torque, it should be disregarded and the nut tightened to the
recommended torque value. If the torque is 1/3 or more of the recommended torque, it should be
added to the recommended torque. Example: The recommended torque is 5070 lb-in. (68 Nm). The
torque at one turn from seating is 30 lb-in. (3 Nm). The correct torque wrench reading would be 80
100 lb-in. (911 Nm).
Retorquing Fasteners. Procedures intended for installing metal fasteners can cause incorrect reading
when used to check or retorque already installed fasteners during maintenance. Before checking or
retorquing an already installed threaded fastener, first mark the fastener and its companion
components so the marks are in line. Second, back it off a 1/4 turn to loosen it. Torque it to the
specification with an even steady pull on the torque wrench. The marks should be in line; if not, the
marks will indicate the fastener was under or over torqued.
Standard Torque Charts. Standard torque charts have been established for dry and wet torque
conditions. Surface variations such as thread roughness, scale paint, lubrication (oil, grease, etc.),
hardening, and plating may alter these values considerably. The following are standard torque charts.
To find the grade of the screw that is to be installed, match the markings on the head to the correct
picture of CAPSCREW HEAD MARKINGS on the table. Manufacturer's marks may vary. These are all
SAE Grade 5 (3 lines):