14 is the biggest for nipples that is safe. A 16 and 18 are safe, just no bigger than a 14, or else you run the the risk of complications. Serious infections can occur and then you run the risk of accidentally pulling it out. I'm sure they go up to 00 some places but they aren't safe.
You can have nipple piercings 00g! I have 2g now and my wife too! the limit is yours nipple size and shape! add a comment
The size of piercings is proportional of the size of nipple iff you have a big nepple you can start with 4gauge and stretch to 00g and more! Search google: Nepple Piercing 0g ore go to BME Piercings add a comment