The public library books, the internet, leather-craft magazines, of course this site, other guilds, friends and Tandy Leather. The main teacher trial and error!
Hi go to a biker leather shop, they should sell them. Most leather vest use line 24 snaps some line 20. The size is approx. 4 to 6 in. long completed, somethimes custom ones are longer. A great way to use scraps, use the curb (?) chain and leather on ends with snaps or all leather with snaps on end.