FAQ: Can thread lengths be extended on a bolt?

FAQ: Can thread lengths be extended on a bolt?


Hi, I’m Gary Rusynyk with Portland Bolt & Manufacturing Company Sometimes our customers ask us if we can add threads to existing bolts. We supply bolts in three configurations: Full-body cut thread, reduced-body rolled thread, and full-body rolled thread. Full-body cut thread is a commonly supplied configuration for large diameter product, long length product, or small quantity runs. In this method, we take full-size round bar, in this case 3/4″ diameter, and we cut the threads. We can extend threads in this situation. We have to put the part back in the threader, line up the threading dies with the existing thread, and the continue cutting threads to the new, desired length. One note though, if the part is hot-dip galvanized, we will need to strip the galvanizing, then re-thread, then re-galvanize. With this situation it may be more cost-effective to just replace the bolts. Reduced-body rolled threads are made using pitch diameter material, which is halfway between the OD of the threads and the root of the threads. The material is then rolled through threading dies, where the threads are formed, rather than cut. In this particular case, we cannot extend the threads. Re-rolling is not an option for us. Some companies may re-roll product, be we are not willing to risk $2,000 in threading dies, re-rolling product. Cutting additional threads will not work, as the unthreaded shank is not full size. With full-body rolled threads, the part is extruded down to pitch diameter, and the threads are rolled back up, so you have a full body. This type of configuration is used with high-volume product and small products such as A325 bolts. When the part is extruded, there is an angle of extrusion, and when you try to re-thread over that angle, you’re going to end up with two or three incomplete threads, which will not meet specification So this part cannot be re-threaded. If you need information on a specific situation, please contact us and we will be happy to tell you what options are available.

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