Take it out and measure it if your piercer didn't tell you. 16g-1.2mm 14g-1.6mm . Its probably one of those but if it isn't look up a gauge-mm conversion.
1.2mm / 16g
Either 16ga or 14ga. Call the shop and see.
Labret is french for lip
It's usually a 16 or a 14 gauge.
Labret studs and any kind of ring are best. You could use an eyebrow bar if you'd like but it can look a bit strange because the ball would point down. Tongue bars are way too long. You could use smaller barbells though, they work just as well as labret studs. Just not the same variety :)
A vertical labret is through the bottom of your lip like a normal labret but instead of the other side being in your lip (touching teeth/on gum) it is through the middle of the bottom lip. so you can see both balls on the bar. See pic: http://www.urbandictionary.com/define.php?term=vertical+labret
A chainsaw can be measured by Engine size or Bar length. Both are important to the weight and cutting applications
If it's a vertical Labret piercing then it's a curved barbell, if it's a standard lip piercing it can be a labret stud or a ring.
The size is selected at the time the piercing is done to best fit the client not all piercings are the same size.
They are called Bio-Plast labret studs, they are a bio-compatable plastic labret stud. www.wildcat.co.uk