Building panels, especially floor panels, which are provided with a locking system including several separate strip parts connected to the panel edge. A strip part, configured to lock panels horizontally and to be fixed to a panel edge, including a strip body with an inner part configured to be fixed under the panel edge and an outer part configured to extend outside the panel edge, wherein the inner part comprises a fixing element configured to lock the strip part to the panel edge in a horizontal direction, wherein the outer part including a locking protrusion, located above the strip body and configured to lock the strip part to the panel edge vertically and a locking element configured to lock the panels in a horizontal direction, and wherein the inner part includes a cavity formed in the strip body and located between the fixing element and the locking protrusion.