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.
Spark plug
Because the spark plug also seals the combustion chamber of the engine when installed, seals are required to ensure there is no leakage from the combustion chamber. The internal seals of modern plugs are made of compressed glass/metal powder, but old style seals were typically made by the use of a multi-layer braze. The external seal is usually a crush washer, but some manufacturers use the cheaper method of a taper interface and simple compression to attempt sealing.