the only thread you can not use in your machine is (hand quilting thread) because it is waxed---i've had a viking for 15 years- i use lots of different threads- everything from cotton, poly, rayon, wool, silk, metallic, aurafil, invisible....as long as you take care of your machine you can use pretty much any thread you want- as long as it's not waxed- (specific for hand work)