This is a simple holder for the Festool 90 Degree Guide Rail Edge Square FS-WA/90
https://www.axminstertools.com/festool-90-degree-guide-rail-edge-square-fs-wa-90-106849 - you can mount it with 3 screws.
I wanted something to hang my edge square on the wall - couldn't find one, so I quickly threw this together.