A thick-walled, heavy-duty aluminium extrusion measuring close to 59 x 22mm with t-slots top and bottom and on one side too. It is only available in 610mm lengths at this stage and being extruded aluminium it can be (carefully) cut on a mitre saw to make shorter lengths if required.
It can be used on its own or in conjunction with the heavy-duty flip stop. To mount it you can mount a bolt to either the bottom or side t-track and bolt through substrate underneath. Alternatively use it in conjunction with the fence t-track mount brackets to clamp into t-track installed in the table underneath.