The SME 309 arm that came with my Model 10A did not have a damping trough, but it did have the VTA setting screw. I once removed the damping trough on my SME V arm for cleaning purposes, and the VTA setting screw was not a part of that assembly. I think the VTA screw and the damping trough are independent.
Tketcham, Are you describing a different arm?
Tketcham, Are you describing a different arm?