This rivet setter is an economical way to set medium rapid rivets, small double cap rivets and medium double cap rivets. However the diameter of this setter is exactly the same size as the medium rivet cap so it may leave a ring around the outer edge of the cap if you don't have the setter exactly lined up with the rivet cap. Rivets can also be set flat without using a rivet setter by tapping them flat with a hammer that has a bit of a convex metal head. Always use a metal anvil or solid piece of steel under the rivet that is on a work surface that will not bounce.
A different setter called the deluxe snap all rivet setter set tool has a wider diameter head that sets the medium rivets perfect without any chance of leaving a ring on the cap. However on the large rivets and extra larger rivets, this deluxe setter is very close the diameter of the cap so you have to be exactly centered so not to leave a ring. Unfortunately our supplier does not sell this deluxe rivet setter separately from this set which makes it expensive if all you want to use from the deluxe set is the rivet setter and not all the snap setters that are included.