925 sterling silver curb chain, available in 1mm, 1.2mm, 1.4mm and 1.6mm thickness (first images from left)
 
16" chains are a good choice for ladies wanting their pendant to sit around the bottom of the neck, like a collar
 
18" chains will sit just below the throat over the collar bone. This is the most popular length.
 
20" chains will sit below the collar bone.
 
22" most suited to gents