Way back in the day before synthetic fly tying materials & rotary vices, when folks tied flies they used silk thread (some still do) & would wax the thread to make dubbing. These days, it's general practice to take a small amount of fur & put it onto the thread by pinching the fur & thread between your thumb & finger, then twisting the two together. With today's nylon threads this works pretty well & will give you a nice clean tapered fly body.
For bushier, buggier bodies of fur you can make what is called a dubbing loop. This is easily done by taking a length of thread while tying the fly & literally making a loop on from the hook. Fur is then put between the sides of the loop, then the whole affair is twisted together. This will give you a rope that can then be wound around the hook to form the body, or part of the body.
But back when..... It was normal practice to make dubbing ropes separate from the fly hook. They could be made up on their own & later tied onto the fly, just the way someone would tie on chenille or tinsel, or what have you today. Also, because they were using silk thread, which might have been a little thicker than nylon, the color of the thread added to the overall effect of the rope.
One way to do this is to use a jig to make these ropes. This jig is a wooden block with posts (or tacks) at either end to wrap the thread around. There's a notch in the side to hold the thread loop partially open - about 2/3 rds of the way down the side of the block. The fur is added inside the loop, then the loop is closed & wound, or spun, tightly together to make the rope. Once it's done the rope is removed from the block.
The beauty of this method is that these ropes can be stored on cards with notches to hold them & used as needed. Taking the time to make them separate allows you to focus & get them right without messing up a fly in progresses, should you have problems.
Below is a video of author Dave Hughes showing how to do this with the wooden block. It's a long video in which Dave is showing a group all about how to tie the flymph, but it starts out with the making of dubbing. Only the first part deals with what we're discussing here, but the entire video is interesting.