How do you interpret a bolt torque specification table?


Quick Answer

To interpret a bolt torque specification table, read across the columns. The first column specifies the bolt's size in inches, while the second illustrates the bolt's TPI. The third and fourth column show the proofload and clampload, respectively, and the fourth column indicates the bolt's tightening torque in feet per pound. The fourth column is divided into three subcolumns to indicate whether the surface of the bolt is galvanized and waxed, galvanized or plain.

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Full Answer

Bolt torque specification tables are all similar with the exception of ASTM A325 bolts. The first and second column still represent bolt size and TPI, but the third column is for tension. It is subdivided into minimum and maximum tension that can be applied to the bolt. The third column is dedicated to tightening torque, and it is also divided into two subcolumns. The first indicates the minimum and maximum range for galvanized and waxed bolts. The second shows the minimum and maximum range for plain bolts.

Proofload is the maximum amount of stress that can be applied to a bolt before it is damaged. The number represents the amount of force that can be applied before the bolt elongates, fractures or deforms. If a bolt torque specification table does not have proofload listed, assume that it is 92 percent of the yield strength.

Clampload is 75 percent of the total proofload. Clampload information is provided as a safety measure so that those tightening the bolt do not come too close to the proofload number. Exceeding the established proofload can cause the bolt to fail.

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