A device for forming a seal includes upper and lower seal members, and a slider, wherein mating surfaces of the seal members interlock. In at least one embodiment, a lifting rib and closure bar on the slider cooperate with a lifting wing and closure bar groove on the upper and lower seal members, respectively. By moving the slider in one direction, the lifting rib lifts the upper seal member fromthe lower seal member. Moving the slider in the opposite direction causes the upper and lower seal members to interlock. In another embodiment, a slider has an intermediate lateral member connected on one side the slider top, and connected on the other side to the slider bottom. A breakaway sealing device is also provided, allowing a person to break the closed seal. A beginning stop block is alsoprovided that includes a means for securing the upper seal member.