While working on AOSEM alignment yesterday, I noticed that a set screw was missing from the UL AOSEM at the M3 stage of PR2.  In attempting to reinstall it, as it is installed from the bottom up, I dropped the set screw.  After failing to locate it, I had to assume that it had fallen into the HAM-ISI through one of the 1/4-20 thru-holes in the optical table within the footprint of the suspension.  After consulting with Hugh and Jim, we decided it is likely not a problem, but we will conduct a more thorough hunt for it the next time the chamber is available for entry.  For reference, the rogue screw is a #4-40 x 0.112, so about the same size as the average piece of rock salt.