Oakum
Oakum can be used to seal cast iron pipe drains. After setting the pipes together, workers pack oakum into the joints, then pour molten lead into the joint to create a permanent seal. The oakum swells and seals the joint, the "tar" in the oakum prevents rot, and the lead keeps the joint physically tight.
Today, modern methods, such as rubber seals (for example, gaskets or o-rings) are more common.
Plica (sigillography)
The purpose of the fold is to provide a more secure anchorage for the seal, and to guard against the parchment being torn. Slots were normally cut in the double thickness of parchment, a cord or tag of parchment threaded through them, and the seal attached to that.