Aside from the superb polish, the greatest thing about these is that the setting around the outside is really small so more of the gem shows.
The below gem measurements are approximate: 6g has an 8mm gem. 4g has a 9mm gem. 2g has a 10mm gem. 1/2" has a 16mm gem. 3/4" has a 23mm gem. 1" has a 30mm gem.