Oakum
Oakum is a preparation of tarred fibre used to seal gaps. Its main traditional applications were in shipbuilding, for caulking or packing the joints of timbers in wooden vessels and the deck planking of iron and steel ships; in plumbing, for sealing joints in cast iron pipe; and in log cabins for chinking. In ship caulking, it was forced between the seams using a hammer and a caulking iron, then sealed into place with hot pitch.
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.