These stud earrings are made with Sterling Silver stud posts.  They are 4mm gemstones and overall earring width is just over 1/8".  
 
Gemstone options are Amethyst, Sapphire (lab created), Peridot, Aquamarine, Tanzanite, Yellow Topaz, Rhodolite Garnet, Blue Spinel, Emerald (lab created) and Pink Zirconia (Zirconia is a Created Stone and the best simulated diamond in the world.