Top mount roller for sliding closet door

The only markings on this is a pat pend stamp. This roller mounts on the top of a wooden sliding closet door with three wood screws down into the door. In the second photo above, the "axle" that points out toward you as you look at it should have a nylon roller on it, but it is totally either worn or broken off. As a result, the door wont slide very well. The bolt that angles up is the adjustment for the roller, using a straight blade screwdriver.

Help me find a replacement. Thanks.