For your reference, BY/DJO's earrings sizings are divided into 4 categories:
Mini : less than 1cm
Small : 1cm to 1.2cm
Medium : 1.3 - 1.5cm
Large : 1.5cm and up
Sizings for the other accessories can be found on their each individual pages.
BY/DJO's earrings are made of  various materials depending on each and every earring. Each will be written at their product page.
They are either gold plated (meaning there is a thin layer of gold plated over a base metal (brass, copper etc), vermeil (a layer of gold plated over sterling silver) or gold filled (real gold permanently bonded to a base metal (brass or sterling silver) and never solid gold.