Usually high-grade galvanized steel for load-bearing stability.
If you are looking for this part because a piece is missing or broken: 888.31.31.497903_403800.it.
When installing parts from the series, avoid using power drills. The particle board in PAX frames can strip easily. Hand-tighten to ensure the bracket sits flush against the frame. 888.31.31.497903_403800.it.
It often serves as a metal bracket, rail connector, or specialized screw assembly required to secure internal shelves or drawers. 888.31.31.497903_403800.it.
Locate your specific furniture's Assembly Instructions PDF on the IKEA website. The part number will be listed in the first few pages under the "Parts List" section.
You can often order small IKEA spare parts for free via the IKEA Spare Parts tool.