Sigma PVP-S4 PV-LOK™ 4" Pipe to Pipe Restraint incorporates a series of machined serrations that effectively engage PVC pipe walls, to provide positive joint security and full support of the pipe. The directional gripping action maximizes restraint during increased line pressures such as those resulting from surges and water hammers. The Series PVP incorporates two PV-LOK clamping rings and a series of restraining rods & nuts that tie the two rings together and secure the PVC bell and spigot pipe joint.