Passing threads are smooth and durable, and are made by wrapping a gold metallic thread around a core. Smooth passing threads are shiny with a smooth appearance. This is accomplished by wrapping a wire around a cotton core keeping it's smooth, even appearance. These are couched into place.
Rococco are shiny with a wavy appearance. This is accomplished by wrapping a wire around a cotton core in such a way that is pulls the cotton core slightly, creating the wavy or bumpy appearance. These are couched into place.
Also available are Flatworm, Check Threads, Japanese Gold Threads, No 7 Tambour, "T" Threads, and other couching threads.