I used to have a Levin (25years ago) that had 6 screw in bridge pieces that were screwed in and out using a slot cut in the truss rod adjusting spanner that came with the guitar. the idea was good but the screw in peices were nylon and the saddle bit tended to chew up if you were carelesswith the spanner. It was the only one that I have ever seen like this. Don't know if this was the only one in existance.