Singer 115 arm side cover #55513 with thumb mounting screw #138E.  With face plate, complete #55644.  Face plate includes thread tension dial and thread guides plus mounting screw #190J.  Price includes shipping to lower 48, return for refund if fails on your 115 restoration.  Both plates etched with flowers and leaves design of model 15.  Plates will work on models 15 as well as 115.