I don't know if any of you are button experts, but I could do with some help! I'm wanting to find out what this style of button is called, but I can't find any sort of terminology that could help me source a match. It's from a vintage garment but I'm sure it's possible to source the same type nowadays. They're flat shank buttons with a deep ridge, but I don't know if this ridge, or style of button, has a name. Any ideas?