Sorry for the confusion - I have heard people refer to synthetic cords as "catgut" since the newer versions were meant to replace the original natural materials - personally I don't think I have ever seen real catgut and so would hesitate to identify it.

Also - you can post items for sale on the Classified page of this forum - I think you have to register separately for it.

Some sharper images and exact measurements would help your ad.

Good luck!