by rmf17
 P: 6 Can any one offer a method or location of a method for determining the permissible axial load that can be applied to an internal thread? i.e. Take a nut and screw into it two bolts, one from either end so they meet in the middle of the nut, then apply a tension force across the two bolts. How much tension can be applied before the thread brakes? The nut in this case is not stamped with its rating or grade etc. Its of a known material with a known tensile and proof strength. I'm not interested in pre-tension caused by tightening, as it is hand tightened, really just like to know how much load can be applied in direct tension. Any offers?
 P: 2,055 The answer is totally variable, as bolts aren't designed to be half screwed into a nut, you'll get massive variation between similar bolts due to tolerances. When a bolts thread is fully engaged, the threads can deform to allow load sharing. If you only engage a couple of threads, they will just strip. So the answer will be 'not a lot' compared to bolt used properly. The only way to find out is to test it. Why on earth are you screwing two bolts into one nut anyway?
 P: 6 Sorry for the confusion. The bolt example is only given as an analogy. What I have is in fact a components that goes on an underground drill rig. The analogy is correct in that what I have is an internally threaded component. There are two internal threads, each of a different diameter, each at a different end of the device. What I'm looking for is a recommendation for a method, or source of method to work out how much load can be applied to this device in axial tension before the thread is stripped. i.e. component critical failure. For structural or civil engineers it's similar to a tie between two threaded tie rods. Round two?
 Sci Advisor HW Helper PF Gold P: 6,050 Calculating maximum load on a thread If the internal thread is deep enough to develop the full strength of the threaded rod screwed into it, then the axial load is limited by the strength of the smaller diameter rod, or the strength (wall thickness) of the threaded device (sleeve). Typically, a 5/8" diameter bolt needs to have a minimum of 5/8" internal thread in the nut (or sleeve), a 2 inch diameter bolt needs 2 inches of thread, etc.
 P: 490 In every job I have ever had it was a requirement that the male member had to fail before the female. But if the designer had other intentions, that may not be so. Not enough information here to know for sure one way or the other.
 P: 125 Sorry that I do not answer your qwestion - because I do not have an answer, but I have thought about this also. I presume, at first, the area of the contacting surfaces (nut thread/bolt thread) need to be calculated. From the force applied, friction loss is to be subtracted. Then you look up at the material (metal) strength.
 P: 100 I also do not have the exact answer, but just suggesting one thing that consider the fact that initial threads engaged are the ones which bear maximum load. So you may want to focus on first few engaging threads instead of whole length of threads