I just happened to see this old topic. Gimp refers to a thread with a core, in recent years a cotton cord core, but also wire cores. Another thread is wrapped around the core. During the 1940s I believe the wrapping thread was usually rayon. Earlier gimps often had silk wrappings. I do not know about modern equivalents -- Kathy is right that the 1940s gimp is about the equivalent of a size 3 thread. It was a stiff thread for making purses and hats. If you do not mind an artificial look you may want to look into some of the modern nylon threads, or even nylon mason's line.