It looks somewhat like an illustration from some instructions for splicing a rope- a modern one, with a cover. If you go here and check out Locking 12 Strand Splice, you will see what I mean. That would make it rather modern, though, and there's something about this that seems older than Dacron. The rope ( if that's what it is) also seems quite large- perhaps it's meant to help illustrate a large rope that's been wormed, served and parcelled?

Anyway, this is at best an educated guess, so if anyone has a better notion I'll delete it.