Studs are designed to be fitted only "finger-tight" into their threaded hole in a casting. However, a locking type of nut (PTN, or prevailing torque nut) is often specified to go on the stud. These two facts present an inherent dilemma. The grip of the PTN on the stud can easily turn the stud when you don't want it to (how often have you removed an exhaust manifold nut and had the stud come out at the same time?)

With this in mind, the installer may be tempted to over tighten the stud into the hole, to make certain it stays put. This mistake happens a couple of ways: Either the stud gets torqued after it bottoms in the hole, or the stud's shoulder (unthreaded section in between the threaded ends) jams into the surface at the edge of the hole. Some studs have no shoulder (all thread), and some holes have no bottom (through hole). This allows for another problem: with nothing to stop it, the stud can insert too deep.

So, why is it wrong to tighten the stud into the hole? Unfortunately, I have even seen it done by supposed "professionals". The way a stud can outperform a bolt in clamping efficiency has to do with the even distribution of stress across the engaged threads. If you torque a stud into a blind hole, you lose that benefit, and concentrate stresses at the first thread in the hole. If you torque the shoulder of a stud against the edge of a threaded hole, you lose the benefit & usually distort the mating surface. It's not as if there is a suitable bearing surface to take the load. Just don't do it.