French wire (or ‘gimp’) is a very tight hollow coil of very fine wire. Your silk thread goes through it at each end. It helps prevent the clasp rubbing through the silk cord and breaking the necklace. It comes in the following sizes: Fine - for Perlseide size 0 - 3, Medium - for Perlseide 4 - 6/7, Heavy /Extra Heavy - for Perlseide 8 and above. You can choose to use a medium french wire on a fine silk cord if the extra thickness will suit your look better.