Gilt Pearl Purl is available in a range of sizes from Very Fine (the finest), through to #4 (the thickest). While this thread is hollow, it is designed to be couched on the surface of your fabric. The thicker threads can be couched without stretching prior to use – the finer threads (#1 and below) need to be stretched to open up the coils to accommodate the Gutermann thread couching it down.
(Photo shows clockwise from bottom left – #3, #2, #1, Super, Very Fine)
(Second photo shows #4)