These are punched from sheet the same way scales are. The holes can position is set, so it's even in regards to the other holes, but can change slightly on the disc. It did not affect the way I used these in the clothing pieces I have made.
Shelley recommends using Stainless Rings to join, as they never tarnish and are strong. The discs are super light weight, the the stainless give the pieces a little weight. Ring size is your choice... I used 18g 3/16" for the piece shown here!