LO 9-8 Outline maintenance procedures and practices used to service diesel engine cylinder heads

Studs Versus Bolts
Some applications or high-performance cylinder head modifications use studs rather than bolts. There are several advantages to using studs. First, studs are often made to higher tensile strengths than stock bolts, permitting higher clamping forces. Also, a stud installed in the cylinder head is far less likely to break when removed.

Studs also can provide an even more consistent clamping force than bolts. With threads at each end, studs are initially finger-tightened into the block. After the cylinder head and gasket are installed, torque is applied to a nut. Unlike a bolt, which is reacting to two separate twisting forces on the bolt head and threads in the block, the stud will stretch only on the vertical axis when the nut is tightened. Rotational force on the stud is avoided and clamping force is directly transferred from the torque applied to the nut. This provides a more even clamping force on the cylinder head.