In 3.81, I was crafting some skis and noticed that it asks for 5 ft of tying equipment, and the text says that rope, cord, or withes can be used. However, spruce withes and birch withes only come in 4 ft increments, and when I try to use a pile of multiple withes, the game displays red text that says "That spruce withe (4 ft) is too short for the purpose." Withes are not able to be joined together like cords can, so there just isn't a way to actually use withes, as far as I can tell.