i want to purchase a grommet machine but i would like to know what is the thickest matieral i can put a grommet through. example what if by chance a customer wants 1/4 in media with grommets ( more than likely never happen just want to know)
You are only limited by the length of your grommets and the throat opening of your grommet press. On some materials and with some grommets you may have to manually drill or punch the holes, depending.
Grommets in fabric material, such as banner material, provide an anchor point with sufficient surface area so as not to pull out of the material. Grommets in rigid materials, such as coroplast etc, mitigate abrasion and pulling out of the material is usually not an issue.
If you're in the market for a grommet press, understand that they all do the same thing in the same way. The only real difference between machines is throat depth and the quality of the die. The die is precision machined to provide just enough, but not too much, friction to hold the grommet over the media. Pacific rim knock offs often have such poorly made dies that they have to work upside down, with the die on the bottom and the anvil on the press. These are a bitch to use requiring two or more steps, even with self piercing grommets and, in general, aren't worth having around.