Studded leather

[Sierra Katrian]

It really depends on the look you are going for. There is no minimum, or maximum size, just make sure that they are no more than 2 inches apart (measured from the centre of the stud)

Find ones that appeal to you, and go with those. If you absolutely need a specific measurement, then go with something in the range of 1/4 inch, or 5/16ths of an inch.