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There will be instances when it’s essential to discover the torque value of a bolt, especially a bolt that has already been installed. Your fastener distributor will recommend using a torque gauge to read the bolt, but you must know when that reading is accurate.
To check how much torque has been applied to a bolt after it has been installed, use a torque gauge and note the reading when any of these three conditions exist:
A. Often called the ‘Crack On’ method, note the reading when the socket starts to move beyond the tightened position in a clockwise direction.
B. Often called the ‘Crack Off’ method, note the reading when the socket starts to move beyond the tightened position in a counter clockwise direction.
C. Often called the ‘Marked Fastener’ method, you’ll initially need to mark both the socket and the joint material to create a point of reference. Back off the nut by 30 degrees and re-tighten to the mark, noting the reading at that match point.
The first two methods will not give as accurate a reading as the third, since static friction is present for both the Crack On and Crack Off methods. Your fastener distributor will likely recommend using the marked fastener method in order to obtain the greatest accuracy. There may be some discrepancy due to gasket creep.
When using any of the three methods above, it’s important to apply torque slowly and deliberately. This ensures that any dynamic effects are controlled and minimal.
Always be sure the bolt is held completely steady when checking the torque. Also, check torque levels before applying any paint or other forms of treatment, such as lubrication or heat. The sooner you check the torque value after installation, the more accurate reading you will obtain.
Your fastener distributor understands that precision and specifications are vital when dealing with equipment and machinery. They are ready to offer advice and direction about how to handle fasteners and fastener components, and how to check torque values after installation is only one of the many tidbits your fastener distributor has to offer.