When shopping for body piercing jewelry, gauge is an important measurement to know. Gauge simply refers to the thickness of the wire that's used for the piece.
Navigating the world of gauges can be a scary place. I remember shopping in retail stores after my own nose piercing healed and I didn't have a clue what I was doing. I was pierced with 18G and wore a screw end. I bought everything from thin 24G to thicker 18G and had a really hard time getting a good fit (no surprise).
So what's there to know? Gauges run opposite, so that the higher the number, the thinner the wire. Most nose piercings are done in 18G to begin with. 18G is a little thicker than most regular earring posts. Earring posts (except the kind you're pierced with) are normally 20G. Personally, I found 18G to be a bit much inside my nostril and I chose to "gauge down" to 20G fairly soon after I started changing out my jewelry. ("gauging down" refers to the process of wearing thinner jewelry and allowing your piercing hole to shrink around it).
I make pieces from a very thin 24G to a thicker 18G as a standard order. I do, however, offer 16G on request. Very few people have 16G nose piercings, so we always have a conversation about the sizing to make sure it's what they really need.
In Europe, the gauge is indicated in millimeters. The conversions are as follows:
24G = .511mm
22G = .644mm
20G = .812mm
18G = 1.02mm
16G = 1.2mm