This stainless ball earring posts ear stud have a 4mm ball. This is a nice size for smaller to medium sized designs. It is not too obstusive but just large enough to add some design to the earring.
They have a closed 2mm loop for hanging earring chain and charms. Note that it is a closed loop so you will have to attach something that you can open such as a jump ring or a wired component.
The pin, or part that goes through the ear lobe, is 11mm long and is about 0.7 mm thick. This is roughly 21 gauge making it very sturdy.