Okay, just to clarify. When I mentioned "unwound gut strings" I meant that the gut core is not wrapped in metal (i.e. usually silver or aluminium, but sometimes gold, tungsten or other metals). The most common gut core strings these days are wrapped with silver or other metal. But there are some dedicated baroque period musicians who will buy "straight" gut strings which are twisted (similar to the clock lines) but minus the metal wrapping found on most strings used these days. There is one place I found online that sells them. They sell them by the foot and you cut them to fit your instrument. However, by far the most common strings among today's string players are synthetic core strings (usually nylon, perlon, zyex) that are wrapped in aluminium, silver or gold. The offer a nice compromise between steel strings and gut strings. Foir ibnstance the ones I use are nylon core wrapped in sterling silver.
I had to do a little reference work to fully understand what you meant by longcase clock lines. Pretty nice clocks. I am mainly into vintage or antique pocket watches but I am beginning to develop an interest in clocks. Some of the long case clocks are stunningly beautiful and I guess they command a nice price. I would love to have one someday. True works of art both in their mechanics and in their fine enclosures and grand designs. Apparently many clock restorers are still using the old type gut clock lines as I noticed a several sites have them available for sale. And in such an application if properly cared for they should last for years. Reminds me of the old gut tailpiece loops on violins that are used to hold the tailpiece in place. These days they use a threaded synthetic (plastic) loop but in the old days the loop was made of a knotted piece of heavy gauge gut string which carries the full stress of the strings. I seen violins well over 50 years old (some over 100) and the gut tailpiece loop is still holding fine with no signs of wear. Indeed a strong material. Would love to chat more about the long case clocks. Sounds very interesting.I forgot also that longcase (Grandfather) and Vienna clock lines were traditionally made from gut. I used it in my clock but often substituted a twisted nylon look-alike when repairing other people's clocks if I knew they were not going to look after the timepiece. I made my clock about 18 years ago and have only applied a little oil to the lines twice since. There's no sign of wear or fraying though mine runs with two 10lb weights whereas others can use up to 14lbs each side. It seems the longcase lines can last for 50 years or more.