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.
Knuckle thread
This thread form's good debris tolerance is the source of its use in oilfields, where it provides a leak-free connection in field use. Many European automobiles use a knuckle thread for their "tow eye," an external threaded recess where a steel towing lug can be fitted. For example, some Porsche cars use DIN 405 Rd 20 x 1/8", and some BMW use a thread similar to DIN 405 Rd 16 x 1/8".
Other applications use a knuckle thread's rounded edges to reduce the stress on softer materials at a point of connection. Some linear actuators use a knuckle thread to reduce the wear of the steel leadscrew against a plastic sliding nut. Firefighting respirator standard EN 148-1 "Respiratory protective devices - Threads for facepieces" lists a knuckle thread to connect metal and rubber parts.