5mm Silver Eyelets
Eyelets, also called small grommets are a ring inserted into a hole through material, such as fabric, paper and card.
I discovered they were called grommets in the US many moons ago when in my first job designing for American Eagle Outfitters in New York, a room full of people stared blankly at me when I was going through my skirt designs saying that the hem had eyelets in! After an embarrassing silence and me turning red and getting flustered trying to describe what they looked like, a designer friend of mine said "Oh! You mean grommets".
These are silver coloured steel eyelets with a 5mm hole in the centre. You can buy them individually or in sets from haberdasheries and craft stores. If you are using 5mm eyelets for the first time you are best to buy them in a set with a simple punch that can be struck with a hammer to set the grommets in place.
If you plan to do a lot of eyelets there are also dedicated eyelet presses with punch and anvil which I find easier and quicker to use, you can also swap the tool attachments in and out of the eyelet presses to suit your eyelet size.