adjustment screws

Hello there. I'm afraid I'm not clear what part you are referring to. If you are talking about sliding glass doors, the adjustment screw adjusts the actual height of the roller. This is necessary to use when removing and replacing the sliding glass door; it also adjusts how the roller runs on the track, and allows for some leeway if a replacement roller has a slightly different wheel diameter than the original (usually within 1/4"). Let me know if you have any other questions.