Correct and incorrect grip lengths

To choose the correct replacement for an unserviceable bolt, you must consider the length of the bolt. As shown in figure 5-1, the bolt length is the distance from the tip of the threaded end to the head of the bolt. Correct length selection is indicated when the bolt extends through the nut at least two full threads. See figure 5-2. If the bolt is too short, it will not extend out of the bolt hole far enough for the nut to be securely fastened. If it is too long, it may extend so far that it interferes with the movement of nearby parts. In addition, if a bolt is too long or too short, its grip will usually be the wrong length. As shown in figure 5-2, the grip length should be approximately the same as the thickness of the material to be fastened. If the grip is too short, the threads of the bolt will extend into the bolt hole. The bolt may act like a reamer when the material is vibrating. To prevent this, make certain that no more than two threads extend into the bolt hole. Also, make certain that any threads that enter the bolt hole extend only into the thicker member that is being fastened. If the grip is too long, the nut will run out of threads before it can be tightened. In this event, a bolt with a shorter grip should be used. If the bolt grip extends only a short distance through the hole, a washer may be used. A second bolt dimension that must be considered is diameter. As shown in figure 5-1, the diameter of the bolt is the thickness of its shaft. The results of using a wrong diameter bolt should be obvious. If the bolt is too big, it cannot enter the bolt hole. If the diameter is too small, the bolt has too much play in the bolt hole. The third and fourth bolt dimensions that should be considered when you choose a bolt replacement are head thickness and width. If the head is too thin or too narrow, it might not be strong enough to bear the load imposed on it. If the head is too thick or too wide, it might extend so far that it interferes with the movement of adjacent parts. AN bolts come in three head styles—hex head, clevis, and eyebolt. NAS bolts are available in 5-2 ANF0502 BOLT GRIP LENGTH CORRECT BOLT GRIP LENGTH TOO SHORT BOLT GRIP LENGTH TOO LONG Figure 5-2.—Correct and incorrect grip lengths. ANF0501 DIAMETER LENGTH THREADS GRIP HEAD WIDTH HEAD THICKNESS Figure 5-1.—Bolt terms and dimensions.