https://www.gobilda.com/1205-series-dual-block-mount-2-1-2-pack/

This Dual Block Mount is incredibly versatile as a joining piece for 1143 Series Mini Low-Side U-Channel. Threaded holes on all sides of the Dual Block Mount’s two blocks allow for the connection of segments of 1143 Series Mini Low-Side U-Channel to other components via M4 screws.