I've seen these guys who have a device usually on a fender telecaster, that will stretch out the b string. It's basically a knob that goes on the butt end of the guitar and is attached to the guitar player. So when he pulls on this knob it makes the guitar kinda sound like a steel. It's usually used in Country music. If anyone can explain what this is, and if u can buy a guitar with it or if you have to make it yourself, that would be appreciated. Thank you!