Serving line was all different diameters. Large ropes required large diameter line. A shroud might require 3/16' or 1/4' diameter line. A 1/2' rope might use a 1/16' or 3/32' diameter line. They made and used whatever was required to do the job. That is what the modeler is supposed to do. For models, fisherman's fly tying 'silk' works great. An internet store called 'theflyshop.com' (they have an on-line and a paper catalog. Look for the fly section.) has everything you will ever need; been buying there for 40 years. By the way , the material is called 'silk' (this was the original material hundreds of years ago) but it is now made from several material types from kevlar to various plastics. There are probably 50 different colors. Use earth colors and don't use pink, etc, your model is not really a starving fish. There are a dozen sizes (size 3 is usually too large. Start with size 6 and go down in size. This material is straight laid and has no twist and goes on flat; exactly what you need in projects this small. I use a lot of size 14 kevlar in a dark yellow-ish color for serving blocks into bights of line; this color looks darker when applied and resembles new rope. I also use light brown, medium brown and dark brown. It costs about $4 for a spool of 200 yards. I use maybe 2 spools total on a 1/4' scale model. Buy 2 spools each in sizes 6,8,14 in the 4 colors and you are set for a decade. Hope this helps.
