Keep in mind that it must be able to get 4 sockets in the first place, then the chance will be just 1/4.1 Tal Rune + 1 Amn Rune + 1 Perfect Ruby + Normal Shield = Socketed Shield of same type
The number of sockets created will vary. The item must be normal and unsocketed. Low-quality items and superior items do not work. The item gets 1-4 sockets, randomly. However, the number of sockets is then restricted by the maximum number of sockets that base item with that ilvl can have. For example, if you have an item that can only have 2 sockets, there's a 3/4 chance of getting 2 sockets and a 1/4 chance of getting 1 socket.