Get a great deal on the Heatlink 78400 Twistseal Supply & Return Module with the plumbing professionals at PlumbersStock. The supply module provides on/off manual control to allow isolation of individual loops, and may be fitted for electric actuator and thermostat operation. The return module permits the balancing of the flow rate. Comes with o-rings. Modules can be locked in place with a couple of turns. No threaded rod, solder, or tools required. Just twist and seal. Heatlink is a popular plumbing brand among both homeowners and contractors for good reason.