Mine was missing too - so here is what I did - I took the mirror to my local hardware store - you know the local True Value where they have the whole row of small screws, etc. in the pull out drawers, found a brass set screw that matched the threads perfectedly, but it was much too long, bought two and took them home. Mounted screw in plastic clamps in vice and took my fine hacksaw blade - cut to desired length - 30 seconds later it is a perfect set screw. I used the hacksaw blade to cut a groove in the top of the screw for my fine common screw driver and mounted it. Has worked like a charm ever since.