Typicall megalugs are used at valve, tee, bend connections. These essentially replace your standard gland follower and gasket setup. Function the same way...sucked tight to seat the gasket and torqued, then you set the megalugs which grab into the ductile iron and lock the joint together. These provide the joint restraint. Historically people used the standard gland and follower and then poured a thrust block behind the tee and hydrant. Some places make you do both, megalugs and thrust blocks. At the piping run joints they can make you use bell restraints...which is basically a megalug on the spigot side and bell restraint on the bell side. These two components are rodded together to restrain pipes in the main run. AWWA publishees table for how many feet of restrained joint you need after each fitting.