Jacket snaps are composed of four pieces. You can see these parts in the picture of jacket snaps further up this page. In the picture going from left to right is the socket, the cap, the stud and the post.
First you need to make the holes in the leather for the snaps with a leather hole punch tool set. We put a piece of scrap leather under the good piece of leather you are punching through. This will act as a cheap disposable cutting pad so the cutters won't dull on the hole punch in the way it would if you punched into a hard surface.
First put the cap through the hole on the finished side of leather and turn is upside down on top of the dot - rivet anvil. Next put the socket on and set it with the snap setter. If you are using a line 20 jacket snap you will need a line 20 baby dot snap setter. If you are using a line 24 snap, you will need a line 24 durable dot snap setter. The same dot - rivet anvil is used for both.
In the other hole, push the post up through the underneath side of the leather and put it on a solid metal surface like a mini anvil or flip the dot - rivet anvil upside down so the flat side is facing up. Next put the stud on top and set it with the appropriate size snap setter. When you hit the snap setter with a hammer, the two parts are held together when the post mushrooms out over the stud.
Line 20 snaps work well in 3 - 4 oz leather thickness for things like change purses. For a bit thicker leather (5 - 6 oz) like that used in a jackknife case, we could use either the line 20 snap or the line 24 snap with regular post. If you get into 8 - 9 oz leather thickness for belts, you will need the line 24 snap with the long post. If you want to use the regular post, you would have to thin the belt leather.
Leather thickness is measured in oz (ounces). 1 ounce is about 1/64 inches thick. Following are some conversions for leather thickness in oz to inches: 3 oz = 3/64", 4 oz = 4/64", 5 oz = 5/64", 6 oz = 6/64", 7 oz = 7/64", 8 oz = 8/64", 9 oz = 9/64"