6mm is equal to a 2 gauge.
18-16 Gauge
I'm guessing 14 gauge.
Normal ear piercings are 18 gauge.
Whenever you go in for a Monroe piercing, the piercer will take a needle, usually either a 18-16 gauge, and pierce your lip with that. It doesn't leave a big hole at all. But, if you want to gauge your Monroe, then you could have the piercer pierce with a bigger gauged needle, or just gauge it out yourself.
Yes
Once any piercing is *seasoned (*over a year old ), so long as the jewellery is appropriate for the piercing in gauge and length or diameter the piercing will not stretch unless you change it to a larger gauge. So will you have this big gaping hole in your lip? Well no, if you stay with the jewellery you are sized to it should stay the same size during the *life of the piercing (* this is for however long you choose to keep the piercing ).
A 14G tongue piercing is bigger than a 16G tongue piercing. The "G" stands for gauge, with a higher number indicating a smaller diameter. Therefore, a 14G piercing is thicker than a 16G piercing.
18 or 20 gauge
yes
You should use a taper. You can probably find these at a piercing studio. It is important to first stretch it to a 16 gauge, and then to a 14 gauge about a month later to prevent tearing.
18 Gauge