Hey guys!

I've got two hauberks I'm comparing from eBay. They are both galv (zinc) and dome head riveted (I assume).

One is by all_beststuff and is 18 gauge/9mm.
One is by gifts_mart and is 16 gauge/10mm.

In your opinion, lower gauge or smaller diameter? Any exp with these people's armour is welcome as well.

Thanks.

I'd say smaller diameter.
I've dealt with all_beststuff before and they're pretty good. They were polite, quick to reply (a couple of days or so), and they offered suggestions on how to go about sizing and their products.
For example they were willing to alter the size of the haubergeon I bought, and with discussion gave me a reasonable price inclusive of postage.
I haven't dealt with them for a while though.
As has been mentioned before, it does come down to what you intend to use it for. And in the end it's not really real mail, so getting it as reasonably priced as you can is a pretty good idea and communication is key.

I took a glance at both shirts on ebay, and having seen both I would definitely recommend the 16ga. one. The reason is that there is more metal around the rivet hole due to the thickness of the wire. This means a greater resistance against impacts, which is what armor is supposed to do. The difference in ID should be a minor issue due to the thicker wire, but the 16g one will be heavier.

If you plan for your armor to see combat, go with the more durable 16ga. hauberk. If you want something lighter and more comfortable for ren faires and the like- and don't plan to get in any actual fights- the 18ga. shirt should be great for you.