"Karat” describes the gold purity of alloys, used in jewelry, like in gold ring settings. Gold is also found in jewelry items such as necklaces, bracelets, earrings, or watches. This expert on the subject gives a great article about this where you can read it and absorb it, or you can get the cliff's notes right here on my blog. As far as terminology goes, “karat” comes from carob, a type of food seed. This seed was positioned opposite end on a scale in ancient times from the gold jewelry. It would measure up against gold , as far as the story goes, to see how much it weighed. Now adays the meaning is a little bit more different as its a purity, not a raw weight. This expert writer says,

"The term 'karat' is a word used to describe the purity of gold alloys, used commonly in jewelry, such as in a gold ring settings or earrings, bracelets, necklaces and watches."

So finally, to answer the question, “What is the difference between kt and ct?” or “What is the difference between karats and carats?” There is no difference. The "kt." version is more popular in the USA, so they say K or kt. for karats, while the ct. version is more popular elsewhere, everywhere else in the rest of hte world. The higher the caratage the better, meaning more gold purity or density. You can find more information about the topic in this expert article from wikipedia.com. See more at: http://www.chacha.com/question/what-is-the-difference-between-10kt-gold-fill-and-10kt-gold#sthash.YIuWv7qP.dpuf